算法| ss 二叉树

• 102.二叉树的层序遍历

102. 二叉树的层序遍历

/**
 * 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[][]}
 */
// 思路
// 使用queue的方式遍历树
// root返回的边界判断
// 缓存length, 不然结果不对;

var levelOrder = function (root) {
  const queue = [];
  queue.push(root);
  let res = [];
  //   root返回的边界判断
  if (root === null) {
    return res;
  }
  while (queue.length) {
    let arr = [];
    // 缓存length,不然结果不对
    let length = queue.length;
    for (let i = 0; i < length; i++) {
      let cur = queue.shift();
      arr.push(cur.val);
      if (cur.left) queue.push(cur.left);
      if (cur.right) queue.push(cur.right);
    }
    res.push(arr);
  }
  console.log(res);
  return res;
};

// 输入：root = [3,9,20,null,null,15,7]
// 输出：[[3],[9,20],[15,7]]