二叉树层序遍历

102.二叉树的层序遍历

每次遍历当前层的所有节点，push下一层的节点即可

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrder = function (root) {
    let result = []
    let curLevel = []
    if (root === null) {
        return result
    }
    let queue = [root]
    while (queue.length) {
        let { length } = queue
        for (let i = 0; i < length; i++) {
            let cur = queue.shift()
            curLevel.push(cur.val)
            if (cur.left) queue.push(cur.left)
            if (cur.right) queue.push(cur.right)
        }
        result.push(curLevel)
        curLevel = []
    }
    return result
};