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Javascript(leetcode#102) Binary Tree Level Order Traversal

發表於 分類於 ， Disqus：

Difficult:Medium

題目

Given the root of a binary tree, return the level order traversal of its nodes’ values. (i.e., from left to right, level by level).

翻譯

給定二叉樹的根，返回其節點值的級別順序遍歷。 （即從左到右，逐級）。

範例

Example 1:
example

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Input: root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]

Example 2:

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Input: root = [1]
Output: [[1]]

Example 3:

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Input: root = []
Output: []

解題思路

1.利用遞迴搜尋
2.依層級加入陣列裡面

Solution

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var levelOrder = function (root) {
    let arr = [];
    let trace = function (root, num) {
        if (root == null) return;

        trace(root.left, num + 1);
        if (arr[num] == undefined) {
            arr[num] = [root.val];
        } else {
            arr[num].push(root.val);
        }
        trace(root.right, num + 1);
    }
    trace(root, 0);
    return arr;
};