Question

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我不了解graph [from]的工作原理，是否在'from'位置检查数组中的值？还是“来自”对象的属性名称？我在终端中都尝试过，当from是一个数字时，使用from作为属性名是可行的。将其用作数组索引会给我一个错误，指出“来自未定义”。还有graph [from] .push（to）。如何运作？

function buildGraph(edges) {
  let graph = Object.create(null);

  function addEdge(from, to) {
    if (graph[from] == null) {
      graph[from] = [to];
    } else {
      graph[from].push(to);
    }
  }
  for (let[from, to] of edges.map(r = > r.split("-"))) {
    addEdge(from, to);
    addEdge(to, from);
  }
  return graph;
}
const roadGraph = buildGraph(roads);

Answer 1

您有一条道路列表，定义为list os字符串对，并以'-'相连，例如"Alice's House-Bob's House"是连接爱丽丝和鲍伯故居的道路。

然后，每条道路都由2条边线合并而成：爱丽丝屋（Alice House）和鲍勃屋（Bob house）（您用split('_')将道路分割为边）。

现在，您创建道路图，这里称为graph。对于每条道路，从点A-> B和点B-> A添加2条边线。

addEdge(from, to);
addEdge(to, from);

因为您可以使用同一条道路双向行驶。

每个addEdge调用都会检查图中是否已经注册了边from。但我认为它应该像这样：

 function addEdge(from, to) {
    if (!graph[from]) { // if object 'from' is not yet register, add an empty array to from key
      graph[from] = [];
    }
    graph[from].push(to); // add edge 'to, to mapping of 'from'
  }

因此最终您将构建一张地图，看起来像这样：

graph = {
   'Alice house': ['Bob house', 'Post office'],
   'Post office': ['Alice house'],
   'Bob house': ['Alice house']
}

Answer 2

点击您喜欢的浏览器的开发工具。在其中输入：

let roadsX = [
  "Alice's House-Bob's House",   "Alice's House-Cabin",
  "Alice's House-Post Office",   "Bob's House-Town Hall",
  "Daria's House-Ernie's House", "Daria's House-Town Hall",
  "Ernie's House-Grete's House", "Grete's House-Farm",
  "Grete's House-Shop",          "Marketplace-Farm",
  "Marketplace-Post Office",     "Marketplace-Shop",
  "Marketplace-Town Hall",       "Shop-Town Hall"
];

function buildGraph(edges) {
  let graph = Object.create(null);
  function addEdge(from, to) {
    if (graph[from] == null) {
      graph[from] = [to];
    } else {
      graph[from].push(to);
    }
  }
  for (let [from, to] of edges.map(r => r.split("-"))) {
    addEdge(from, to);
    addEdge(to, from);
  }
  return graph;
}

let roadGraphX = buildGraph(roads);

console.log(roadGraphX);

您将看到函数的作用。

有人可以帮助我理解此代码吗？

2 个答案: