题目： 有二叉树如下， 按层级输出结果： [[3], [9, 20], [15, 7]]
3
/ \
9 20
/ \
15 7
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
原题链接： https://leetcode-cn.com/problems/binary-tree-level-order-traversal/
解法1： 基于DFS
遍历时，添加第二个参数，记录层级深度
function levelOrder(root) {
let arr = [];
if(!root) {
return []
}
function dfs(node, level) {
if(!arr[level]) {
arr[level] = [];
}
arr[level].push(node.val);
if(node.left) {
dfs(node.left, level+1);
}
if(node.right) {
dfs(node.right, level + 1);
}
}
dfs(root, 0);
return arr;
};
解法2：基于BFS
function bfs(tree) {
let arr = [];
let res = [];
let count = 0;
arr.push([tree]);
while(count < arr.length) {
const nodeArr = arr[count++];
res.push(nodeArr.map(n => n.val));
const nextLevelNodes = nodeArr.reduce((prev, cur) => {
if(cur.left){
prev.push(cur.left);
}
if(cur.right) {
prev.push(cur.right);
}
return prev;
}, []);
if(nextLevelNodes.length) {
arr.push(childNodeArr);
}
}
return res;
}
