leetcode -binaryTreeLevelOrderTraversal

Leetcode题解之 —— 二叉树的层次遍历 II

思路

---

BFS算法

• queue队列辅助
• 内部循环分组
• result反转

题解

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/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrderBottom = function (root) {
  if (!root) {
    return [];
  }

  const [result, queue] = [[], [root]];

  while (queue.length) {
    // 保存分组的值
    const [group, queueLen] = [[], queue.length];
    let count = 0;

    while (count < queueLen) {
      const currentNode = queue.shift();
      group.push(currentNode.val);
      currentNode.left && (queue.push(currentNode.left));
      currentNode.right && (queue.push(currentNode.right));
      count++;
    }

    result.push(group);
  }

  return result.reverse();
}