[LeetCode] 652. Find Duplicate Subtrees

最新推荐文章于 2023-02-25 22:41:55 发布

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最新推荐文章于 2023-02-25 22:41:55 发布

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原文链接：https://segmentfault.com/a/1190000016966012

本文深入探讨了一种高效算法，用于在二叉树中找出所有重复的子树结构。通过序列化节点值和子树结构，算法能够识别并返回所有具有相同结构和节点值的重复子树的根节点。该方法利用哈希映射记录每个子树的出现次数，仅需遍历一次树即可完成任务。

Problem

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.

Solution

class Solution {
    public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
        List<TreeNode> res = new LinkedList<>();
        serialize(root, new HashMap<>(), res);
        return res;
    }
    private String serialize(TreeNode root, Map<String, Integer> map, List<TreeNode> res) {
        if (root == null) return "()";
        String str = "(" + root.val + serialize(root.left, map, res) + serialize(root.right, map, res) + ")";
        if (map.getOrDefault(str, 0) == 1) res.add(root);
        map.put(str, map.getOrDefault(str, 0)+1);
        return str;
    }
}