366. Find Leaves of Binary Tree

🟠   🔖  树 深度优先搜索 二叉树  🔗 LeetCode

题目

Given a binary tree, collect a tree's nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.

Example 1:

      1
     / \
    2   3
   / \
  4   5

Input: [1,2,3,4,5]

Output: [[4,5,3],[2],[1]]

Explanation:

[[3,5,4],[2],[1]] and [[3,4,5],[2],[1]] are also considered correct answers since per each level it does not matter the order on which elements are returned.

Example 2:

Input: root = [1]

Output: [[1]]

Constraints:

• The number of nodes in the tree is in the range [1, 100].
• -100 <= Node.val <= 100

题目大意

给你一棵完全二叉树，请按以下要求的顺序收集它的全部节点：

1. 依次从左到右，每次收集并删除所有的叶子节点
2. 重复如上过程直到整棵树为空

解题思路

二叉树节点的高度的定义是：节点到叶子节点的最长路径（边数），可以发现返回数组其实是按照二叉树的高度来分组的，只需求出每个节点左右子树的最大深度 - 1，即是该节点的高度。

代码

/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var findLeaves = function(root) {
    if (!root) return []
    let res = []
    const maxDepth = (root) => {
        if (!root) return 0
        let depth = Math.max(maxDepth(root.left), maxDepth(root.right)) + 1
        res[depth - 1].push(root.val)
        return depth
    }
    maxDepth(root)
    return res
}