LeetCode 652. Find Duplicate Subtrees

寻找重复子树算法解析

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本文深入探讨了在二叉树中寻找重复子树的问题，介绍了一种通过序列化处理来识别相同结构与节点值的子树的方法。利用递归序列化每个子树，并借助哈希映射记录序列出现次数，当某个子树序列出现第二次时，将其根节点加入结果列表。

652. Find Duplicate Subtrees

Given a binary tree, return all duplicate subtrees. For each kind of duplicate subtrees, you only need to return the root node of any one of them.

Two trees are duplicate if they have the same structure with same node values.

Example 1:

The following are two duplicate subtrees:

  2
 /
4

and

Therefore, you need to return above trees’ root in the form of a list.

Approach

题目大意：要求你在二叉树中找到相同的子树，包括叶子节点。
思路方法：对树进行序列化处理，中间过程可以获得以每个结点作为根的子树序列，由此判断这些子树序列是否重复，重复则放进vector中。

Code

class Solution {
public:
    vector<TreeNode*> nums;
    unordered_map<string, int>unmp;
    vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) {
        Search(root);
        return nums;
    }
    string Search(TreeNode* root) {
        if (root == nullptr)return "#";
        string str = to_string(root->val) + "," + Search(root->left) + "," + Search(root->right);
        unmp[str]++;
        if (unmp[str] == 2) {
            nums.push_back(root);
        }
        return str;
    }
};