Question

ES6 中的 Map() 错误

2018-06-09

285

javascript reactjs dictionary redux depth-first-search

我尝试在 React、Redux 中实现 DFS 算法以将其可视化。
要创建邻接表，我使用 JavaScript 中的 Map() 数据结构：

dfs(v, visited, adjList) {
  console.log(v);
  visited[v] = true;

  var get_neighbours = adjList.get(v);

  for (var i in get_neighbours) {
    var get_elem = get_neighbours[i];
    if (!visited[get_elem])
      this.dfs(get_elem, visited, adjList);
  }
}

dfsStart(e) {
  var n = 0;
  var adjList = new Map();
  for (var i = 0; i < this.props.edges.length; i++) {
    n = Math.max(this.props.edges[i].u, this.props.edges[i].v);
  }
  for (var i = 1; i <= n; i++) {
    adjList.set(i, []);
  }
  for (var key of adjList.keys()) {
    console.log(key);
  }
  //console.log(adjList.size);
  for (var i = 0; i < this.props.edges.length; i++) {
    var x = this.props.edges[i].u;
    var y = this.props.edges[i].v;
    console.log(x + " " + y);
    [...adjList.get(x), y] - > where I am getting error
  }
  for (var key of adjList.values()) {
    console.log(key);
  }
  var visited = [];
  for (i = 1; i <= n; i++) {
    visited[i] = false;
  }
  this.dfs(1, visited, adjList);
}

我甚至尝试使用 push() 方法将值推送到空列表中，如下所示

adjList.get(x).push(y)

但这也给了我一个错误！

Uncaught TypeError: Cannot convert undefined or null to object at Function.from ()

当我使用 push() 时：

Layout.js:72 Uncaught TypeError: Cannot read property push of undefined at Layout.dfsStart (Layout.js:72)

Answer 1

我猜你想将最大的 x 值放入 n 中，而不是最后一个 x 或 y，请更改：

for(var i=0;i<this.props.edges.length;i++)
  n = Math.max(this.props.edges[i].u, this.props.edges[i].v);

更改为：

n = Math.max(...this.props.edges.map(edge => edge.u));

Answer 2

dfs(v, visited, adjList) {
console.log(v);
visited[v] = true;

var get_neighbours = adjList.get(v);

console.log(get_neighbours);

for (var i in get_neighbours) {
    var get_elem = get_neighbours[i];
    //console.log(get_elem);
    if (!visited[get_elem]) {
        this.dfs(get_elem, visited, adjList);
    }
 }
}



dfsStart(e) {
var n = 0;
var adjList = new Map();
for(var i=0;i<this.props.edges.length;i++) {
  n = Math.max(n, Math.max(this.props.edges[i].u, this.props.edges[i].v));
  adjList.set(this.props.edges[i].u, []);
}
for(var i=0;i<this.props.edges.length;i++) {
  adjList.get(this.props.edges[i].u).push(this.props.edges[i].v);
}
var visited = [];
for(i=1;i<=n;i++) {
  visited[i] = false;
}
this.dfs(1, visited, adjList);
}

这样做可以解决问题，但是当我使用 console.log(get_neighbours) 时，dfs() 函数仍然会出现未定义的错误，