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    1. /**
    2.  * Definition for a binary tree node.
    3.  * function TreeNode(val, left, right) {
    4.  *     this.val = (val===undefined ? 0 : val)
    5.  *     this.left = (left===undefined ? null : left)
    6.  *     this.right = (right===undefined ? null : right)
    7.  * }
    8.  */
    9. /**
    10.  * @param {TreeNode} root
    11.  * @return {number[][]}
    12.  */
    13. var levelOrder = function(root) {
    14.     if(!root) return []
    15.     let result = []
    16.     let que = []
    17.     que.push(root)
    18.     while(que.length !== 0) {
    19.         let init_size = que.length
    20.         let temp = []
    21.         for (let i = 0; i<init_size; i++) {
    22.             let mp = que.shift()
    23.             if(mp.left) que.push(mp.left)
    24.             if(mp.right) que.push(mp.right)
    25.             temp.push(mp.val)
    26.         }
    27.         result.push(temp)
    28.     }
    30.     return result
    31. };

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