102. 二叉树的层序遍历🔖BFS

• https://leetcode-cn.com/problems/binary-tree-level-order-traversal/

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/**
 * 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) {
    if(!root) return []
    let result = []
    let que = []
    que.push(root)
    while(que.length !== 0) {
        let init_size = que.length
        let temp = []
        for (let i = 0; i<init_size; i++) {
            let mp = que.shift()
            if(mp.left) que.push(mp.left)
            if(mp.right) que.push(mp.right)
            temp.push(mp.val)
        }
        result.push(temp)
    }

    return result
};