102. Binary Tree Level Order Traversal

[Tcdian]

102. Binary Tree Level Order Traversal

给你一个二叉树，请你返回其按 层序遍历 得到的节点值。 （即逐层地，从左到右访问所有节点）。

Example

Given binary tree [3,9,20,null,null,15,7]

    3
   / \
  9  20
    /  \
   15   7

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

[Tcdian]

Solution

• JavaScript Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrder = function(root) {
    if (root === null) {
        return [];
    }
    const result = [];
    const queue = [[0, root]];
    while(queue.length !== 0) {
        const [level, node] = queue.shift();
        result[level] = result[level] || [];
        result[level].push(node.val);
        if (node.left) {
            queue.push([level + 1, node.left]);
        }
        if (node.right) {
            queue.push([level + 1, node.right]);
        }
    }
    return result;
};