LeetCode算法笔记-Day51
102. Binary Tree Level Order Traversal
Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).
example:
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| Given binary tree [3,9,20,null,null,15,7]:
3
/ \
9 20
/ \
15 7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]
|
Analyse:
递归
想到递归，我们一般先想到DFS。我们可以对该二叉树进行先序遍历（根左右的顺序），同时，记录节点所在的层次level，并且对每一层都定义一个数组，然后将访问到的节点值放入对应层的数组中。
My Answer：
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| /**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number[][]}
*/
var levelOrder = function(root) {
let res = [];
if(!root) return res;
let dfs = (node,level)=>{
if(!!node){
if(res.length <= level) res.push([]);
res[level].push(node.val);
dfs(node.left,level+1);
dfs(node.right,level+1);
}
}
dfs(root,0);
return res;
};
|
