面试题55 - I. 二叉树的深度

示例

给定二叉树 [3,9,20,null,null,15,7]，

    3
   / \
  9  20
    /  \
   15   7
返回它的最大深度 3 。

JS

1.递归思路

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxDepth = function (root) {
    const treeDep = function (node, n = 0) {
        if (node) {
            let l = treeDep(node.left, n + 1)
            let r = treeDep(node.right, n + 1)
            return l > r ? l : r;
        }
        return n
    }
    return treeDep(root)
};

2.非递归思路 使用层序遍历(BFS)

/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxDepth = function (root) {
    const treeDep = function (node) {
        let level = 0
        let queue = []
        if (!node) {
            return level
        }
        queue.push(node)
        while (queue.length !== 0) {
            let len = queue.length
            level++
            while (len) {
                let n = queue.shift()
                if (n.left) {
                    queue.push(n.left)
                }
                if (n.right) {
                    queue.push(n.right)
                }
                len--
            }
        }
        return level
    }
    return treeDep(root)
};

题链