编程知识 cdmana.com

用 JavaScript 实现寻路算法 —— 编程训练

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\n \n \n
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之前,我们会对 DOM 元素中的格子的背景颜色进行改变,这样我们就可以看到寻路的过程","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","text":"因为我们需要看到这个过程,所以每一次入队列的时候我们需要给一个 1 秒的等待时间,这个就是使用 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"async","attrs":{}}],"attrs":{}},{"type":"text","text":" 和 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"await","attrs":{}}],"attrs":{}},{"type":"text","text":" 的好处。在加入这个背景颜色之前,我们就可以加入一个 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"await sleep(1)","attrs":{}}],"attrs":{}},{"type":"text","text":",这样入队列和改变格子背景颜色之前就会有 1 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| ","attrs":{}},{"type":"link","attrs":{"href":"https://github.com/TriDiamond/frontend-tutorials/blob/master/exercises/path-finder/3-map-search-async.html","title":""},"content":[{"type":"text","text":"查看代码","attrs":{}}]},{"type":"text","text":" | ","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"喜欢的同学 star 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","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"5","attrs":{}}],"attrs":{}},{"type":"text","text":",","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"6","attrs":{}}],"attrs":{}},{"type":"text","text":",","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"7","attrs":{}}],"attrs":{}},{"type":"text","text":" 这三个格子都是从 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"1","attrs":{}}],"attrs":{}},{"type":"text","text":" 这个格子扩展过来的。既然我们知道每个给自上一步的来源,是不是我们可以在每一个给自记录上一个来源的格子呢?所以在代码中我们是不是可以在入队的时候,就记录上一个给自的 x,y轴呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那么我们就产生一个想法,通过这个记录,我们怎么寻找最终的路径呢?","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们假设终点是在 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"8","attrs":{}}],"attrs":{}},{"type":"text","text":" 这个位置,我们过来 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"8","attrs":{}}],"attrs":{}},{"type":"text","text":" 这个点的时候是从我们的起点一步一步扩展出来的,那我们反过来通过记录了每一个格子的前驱格子,就可以一步一步收缩回到起点呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那就是说,从 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"8","attrs":{}}],"attrs":{}},{"type":"text","text":" 开始收,","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"8","attrs":{}}],"attrs":{}},{"type":"text","text":" 是从 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"2","attrs":{}}],"attrs":{}},{"type":"text","text":" 走过来的,而 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"2","attrs":{}}],"attrs":{}},{"type":"text","text":" 就是从","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"起点","attrs":{}}],"attrs":{}},{"type":"text","text":" 扩展过来的,最终我们就找到起点了。如果我们在收缩的过程记录着收缩时候访问到的格子,最终这些格子就是从起点到终点的整条路径了!是不是很神奇?!","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其实也可以理解为一个 “原路返回” 的效果!","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bd/bd95a0f527518180b8a254451db42abe.gif","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先不要鸡冻,稳住!我们接下来看看代码是如何处理的:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"其实基本上我们的代码没有太多的改变","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"首先就是在 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"while","attrs":{}}],"attrs":{}},{"type":"text","text":" 循环当中的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"insert()","attrs":{}}],"attrs":{}},{"type":"text","text":" 调用的时候添加了上一个坐标的传参","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"这里我们顺便也把横向的可走的格子也加入到队列中","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"这里因为我们需要记录所有格子的前驱坐标,所以我们需要声明一个 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"table","attrs":{}}],"attrs":{}},{"type":"text","text":" 的变量存放这个数据","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"在我们进入队列之前,我们就把当前入队列的格子的值存为上一个格子的坐标(这个为了我们后面方便收缩是找到整个路径)","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","text":"最后在 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"while","attrs":{}}],"attrs":{}},{"type":"text","text":" 循环中,当我们遇到终点的 x 和 y 的时候,我们加入一段 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"while","attrs":{}}],"attrs":{}},{"type":"text","text":" 循环","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":7,"align":null,"origin":null},"content":[{"type":"text","text":"这个 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"while","attrs":{}}],"attrs":{}},{"type":"text","text":" 就是往回一直走,知道我们找到起点位置,在往回走的同时,把每一个经过的格子的背景改为另外一个背景颜色,这样就可以在我们的地图上画出一个路径了!","attrs":{}}]}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"好思路清晰,我们来上一波代码吧!","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"// 上一部分的代码,这里就忽略了...\n// 只要在上部分的代码后面改造这部分即可\n\n/**\n * 寻路方法 (异步)\n * @param {Array} map 地图数据\n * @param {Array} start 起点 例如:[0, 0]\n * @param {Array} end 终点 例如:[50, 50]\n * @return Boolean\n */\nfunction sleep(t) {\n return new Promise(function (resolve) {\n setTimeout(resolve, t);\n });\n}\n\n/**\n * 入队方法 (异步)\n * @param {Integer} x\n * @param {Integer} y\n */\nasync function findPath(map, start, end) {\n // 创建一个记录表格\n let table = Object.create(map);\n let queue = [start];\n\n /**\n * 入队方法 (异步)\n * 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","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"while","attrs":{}}],"attrs":{}},{"type":"text","text":" 循环里面我们用了 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"path","attrs":{}}],"attrs":{}},{"type":"text","text":" 做为记录路径的变量。这里还需要注意的就是,我们的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"find","attrs":{}}],"attrs":{}},{"type":"text","text":" 按钮里面的函数调用也需要一并修改哦。","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"html"},"content":[{"type":"text","text":"\n
\n \n \n
","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" ","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"运行最终效果如下:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/eb/eb81f224a7a560665193edbe218d5829.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"http://tridiamond.tech/frontend-tutorials/exercises/path-finder/4-map-find-path.html","title":""},"content":[{"type":"text","text":"查看效果","attrs":{}}]},{"type":"text","text":" | ","attrs":{}},{"type":"link","attrs":{"href":"https://github.com/TriDiamond/frontend-tutorials/blob/master/exercises/path-finder/4-map-find-path.html","title":""},"content":[{"type":"text","text":"查看代码","attrs":{}}]},{"type":"text","text":" | ","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"喜欢的同学 star 一下谢谢!","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"启发式寻路(A*)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"到这里我们已经完成了整个广度优先寻路的算法。但是广搜式寻路是不是最好的寻路方案呢?","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"其实并不是的","attrs":{}}],"attrs":{}},{"type":"text","text":"!","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bc/bc8b68ef9eb75f70203c94c48089c90b.gif","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过各位数学科学家的努力下,他们证明了一件事情。我们是可以有一种方法能够加速寻路的,通过用这个方法我们不需要使用一个非常傻的方式来挨个去找。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这种寻路的方式叫做 “","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"启发式寻路","attrs":{}}],"attrs":{}},{"type":"text","text":"”","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"启发式寻路就是用一个函数去判断这些点扩展的优先级。只要我们判断好了优先级,我们就可以有目的的去验者格子的方向做优先找路。","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"“但是这个找到的路径是不是最佳路径呀?说的那么神奇的。“ 说实话,这个我们普通人的思路就排不上用场了。但是数学家证明了一件事情,只要我们使用启发式函数来估计值,并且这些值能够一定小于当前点到终点的路径的长度,这样就一定能找到最优路径。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这种能找到最优路径的启发式寻路,在计算机里面我们叫它做 “","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"A*","attrs":{}}],"attrs":{}},{"type":"text","text":"”。这里面的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"A","attrs":{}}],"attrs":{}},{"type":"text","text":" 代表着一种不一定能找到最优路径的启发式寻路。所以 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"A*","attrs":{}}],"attrs":{}},{"type":"text","text":" 就是 A 寻路的一个特例,是一种可以找到最佳路径的一种算法。","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"要实现这个启发式寻路,其实我们是不需要改过多我们 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"findPath()","attrs":{}}],"attrs":{}},{"type":"text","text":"函数里面的代码的。我们要改的是我们存储的数据结构,也就是我们的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"queue","attrs":{}}],"attrs":{}},{"type":"text","text":" 队列。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们要把 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"queue","attrs":{}}],"attrs":{}},{"type":"text","text":" 的先进先出变成一个","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"优先队列 (Prioritized Queue)","attrs":{}}],"attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以我们需要构建一个 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Sorted","attrs":{}}],"attrs":{}},{"type":"text","text":" 类,这个类有几个工作:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"这个类可以存储我们之前 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"queue","attrs":{}}],"attrs":{}},{"type":"text","text":" 队列里面的数据","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"可以支持传入排序函数(也就是和我们 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"array sort","attrs":{}}],"attrs":{}},{"type":"text","text":" 函数一样的功能,可以传入一个排序规则函数,也叫 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"compare","attrs":{}}],"attrs":{}},{"type":"text","text":" 函数)","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"在我们通过这个类获取值的时候给我们数据里面的最小值","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"在我们插入数据的时候不需要排序,只是单纯的保存","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"每次去除数据的时候,可以把输出的数据在类的数据里面删除掉","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","text":"这样我们就可以一直在里面获取数据,知道没有数据为止","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":7,"align":null,"origin":null},"content":[{"type":"text","text":"最后加入一个可以获取当前数据的长度(这个在我们的寻路算法中需要用到)","attrs":{}}]}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这里我们用一个非常 “土鳖” 的数组来实现这个 Sorted 类,但是在计算机当中,我们还有很多其他方式可以实现这一种类。比如说 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"winner tree","attrs":{}}],"attrs":{}},{"type":"text","text":",","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"堆 (heap)","attrs":{}}],"attrs":{}},{"type":"text","text":",","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"排序二叉树","attrs":{}}],"attrs":{}},{"type":"text","text":" 等很多的不同思路来实现有序的数据结构。","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"好废话少说,我们来看看怎么实现这个数据结构:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"/** 排序数据类 */\nclass Sorted {\n constructor(data, compare) {\n this.data = data.slice();\n this.compare = compare || ((a, b) => a - b);\n }\n take() {\n // 考虑到 null 也是可以参与比较的,所以这里返回 null 是不合适的\n if (!this.data.length) return;\n // 记录最小的值\n // 默认第一个位置为最小值\n let min = this.data[0];\n // 记录最小值的位置\n let minIndex = 0;\n\n // 开始比较数组里面的所有值,找到更小的值,就记录为 min\n // 同时记录最小值,和最小值的位置\n for (let i = 1; i < this.data.length; i++) {\n if (this.compare(this.data[i], min) < 0) {\n min = this.data[i];\n minIndex = i;\n }\n }\n\n // 现在我们要把最小值拿出去了,所以要在我们当前的数据中移除\n // 这里我们不考虑使用 splice,因为 splice 移除会涉及数组内的元素都要往前挪动\n // 这样 splice 就会有一个 O(N) 的时间复杂度\n // 这里我们用一个小技巧,把数组里面最后一位的值挪动到当前发现最小值的位置\n // 最后使用 pop 把最后一位数据移除\n this.data[minIndex] = this.data[this.data.length - 1];\n this.data.pop();\n // 最后把最小值输出\n return min;\n }\n give(value) {\n this.data.push(value);\n }\n get length() {\n return this.data.length;\n }\n}","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有了这个 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Sorted","attrs":{}}],"attrs":{}},{"type":"text","text":" 的数据结构之后,我们就可以用来解决我们的寻路问题,让我们可以找到最佳的路径了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"加入这个最佳路径的逻辑,我们需要改到一下几个点:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"首先改写我们的存储数据的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"queue","attrs":{}}],"attrs":{}},{"type":"text","text":",使用我们 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Sorted","attrs":{}}],"attrs":{}},{"type":"text","text":" 的排序数据结构","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"编写一个 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"distance()","attrs":{}}],"attrs":{}},{"type":"text","text":" 函数来运算任何一个格子与终点格子的直线距离","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"把所有入队列和出队列的调用改为使用 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Sorted","attrs":{}}],"attrs":{}},{"type":"text","text":" 类里面的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"take","attrs":{}}],"attrs":{}},{"type":"text","text":" 取值 和 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"give","attrs":{}}],"attrs":{}},{"type":"text","text":" 插入值函数","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"其他地方基本就没有什么改变了","attrs":{}}]}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"接下来我们来看看代码是怎么实现的:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"javascript"},"content":[{"type":"text","text":"// 上一部分的代码,这里就忽略了...\n// 只要在上部分的代码后面改造这部分即可\n\n/**\n * 寻路方法 (异步)\n * @param {Array} map 地图数据\n * @param {Array} start 起点 例如:[0, 0]\n * @param {Array} end 终点 例如:[50, 50]\n * @return Boolean\n */\nasync function findPath(map, start, end) {\n // 创建一个记录表格\n let table = Object.create(map);\n let queue = new Sorted([start], (a, b) => distance(a) - distance(b));\n\n async function insert(x, y, pre) {\n // 到达底盘边缘,直接停止\n if (x < 0 || x >= 100 || y < 0 || y >= 100) return;\n // 遇到地图的墙,也停止\n if (table[y * 100 + x]) return;\n // 加入 30 毫秒的停顿,让我们可以看到 UI 上面的变化\n await sleep(1);\n // 给搜索到的路径的格子加上背景颜色\n container.children[y * 100 + x].style.backgroundColor = 'DARKSLATEBLUE';\n // 标记走过的格子的值,标记为上一个格子的 x,y 位置\n table[y * 100 + x] = pre;\n // 把可走的路推入队列\n queue.give([x, y]);\n }\n\n /**\n * 获取格与格之前的距离\n * @param {Array} point 当前格子的坐标:[x,y]\n */\n function distance(point) {\n // 使用三角形 x^2 + y^2 = z^2 的方式来计算距离\n return (point[0] - end[0]) ** 2 + (point[1] - end[1]) ** 2;\n }\n\n // 循环格子 4 边的格子\n while (queue.length) {\n let [x, y] = queue.take();\n // console.log(x, y);\n\n // 遇到了终点位置就可以返回了\n if (x === end[0] && y === end[1]) {\n let path = [];\n\n // 往回走,直到走到起点\n // 这样就能画出最佳路径了\n while (x != start[0] || y != start[1]) {\n path.push(map[y * 100 + x]);\n [x, y] = table[y * 100 + x];\n container.children[y * 100 + x].style.backgroundColor = 'fuchsia';\n }\n\n return path;\n }\n\n // 把上下左右推入队列\n await insert(x - 1, y, [x, y]);\n await insert(x, y - 1, [x, y]);\n await insert(x + 1, y, [x, y]);\n await insert(x, y + 1, [x, y]);\n\n // 把 4 个 斜边推入队列\n await insert(x - 1, y - 1, [x, y]);\n await insert(x + 1, y - 1, [x, y]);\n await insert(x - 1, y + 1, [x, y]);\n await insert(x + 1, y + 1, [x, y]);\n }\n\n return null;\n}","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这个最终的运行效果如下:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/cd/cd7dfa17b40260f1210e225cfb5b1c5c.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"http://tridiamond.tech/frontend-tutorials/exercises/path-finder/6-map-best-path.html","title":""},"content":[{"type":"text","text":"查看效果","attrs":{}}]},{"type":"text","text":" | ","attrs":{}},{"type":"link","attrs":{"href":"https://github.com/TriDiamond/frontend-tutorials/blob/master/exercises/path-finder/6-map-best-path.html","title":""},"content":[{"type":"text","text":"查看代码","attrs":{}}]},{"type":"text","text":" | ","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"喜欢的同学 star 一下谢谢!","attrs":{}}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"horizontalrule","attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我是来自《","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"技术银河","attrs":{}},{"type":"text","text":"》的","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"三钻","attrs":{}},{"type":"text","text":":\"学习是为了成长,成长是为了不退步。坚持才能成功,失败只是因为没有坚持。同学们加油哦!下期见!\"","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f7/f7db8645b6fdfa85351bc5f5aeb79aeb.gif","alt":null,"title":"","style":[{"key":"width","value":"25%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"horizontalrule","attrs":{}},{"type":"heading","attrs":{"align":null,"level":1}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}

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