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Javascript(leetcode101) Symmetric Tree

發表於 分類於 ， Disqus：

Difficult:Easy

題目

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

翻譯

給定二叉樹的根，檢查它是否是自身的鏡像（即圍繞其中心對稱）。

範例

Example 1:
example

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Input: root = [1,2,2,3,4,4,3]
Output: true

Example 2:
example

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Input: root = [1,2,2,null,3,null,3]
Output: false

解題思路

1.利用動態規劃
2.分析if條件

Solution

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var isSymmetric = function (root) {
    let dp = function (left, right) {
        if (left == null && right == null) return true;
        if (left != null && right == null) return false;
        if (left == null && right != null) return false;
        return left.val == right.val && dp(left.left, right.right) && dp(left.right, right.left);
    }
    return dp(root.left, root.right);
};