力扣：652. 寻找重复的子树

原创已于 2022-09-05 23:48:27 修改 · 144 阅读

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#leetcode #深度优先 #算法

于 2022-09-05 23:48:25 首次发布

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该篇博客介绍了一个Java程序，用于寻找给定二叉树中重复的子树。通过深度优先搜索（DFS）策略，将每个节点的子树转化为字符串并存储到哈希映射中。当遇到重复的子树字符串时，将其添加到结果集中。最终返回所有重复的子树节点。

package com.算法专练.力扣.寻找重复的子树;

import java.util.*;

/**
 * @author xnl
 * @Description:
 * @date: 2022/9/5   23:14
 */
public class Solution {
    public static void main(String[] args) {
        Solution solution = new Solution();
        TreeNode node = new TreeNode(1, new TreeNode(2, new TreeNode(4), null),
                new TreeNode(3, new TreeNode(2, new TreeNode(4), null), new TreeNode(4)));
        System.out.println(solution.findDuplicateSubtrees(node));
    }

    /**
     * 使用hash,序列化字符串
     * @param root
     * @return
     */
    Map<String,TreeNode> map = new HashMap<>();
    Set<TreeNode> set = new HashSet<>();
    public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
        dfs(root);
        return new ArrayList<>(set);
    }

    private String dfs(TreeNode node){
        if (node == null){
            return "";
        }
        StringBuilder sb = new StringBuilder();
        sb.append(node.val);
        sb.append("(");
        sb.append(dfs(node.left));
        sb.append(")(");
        sb.append(dfs(node.right));
        sb.append(")");
        String serial = sb.toString();
        if (map.containsKey(serial)){
            set.add(map.get(serial));
        } else {
            map.put(serial, node);
        }
        return serial;
    }
}

class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;
      TreeNode() {}
      TreeNode(int val) { this.val = val; }
      TreeNode(int val, TreeNode left, TreeNode right) {
          this.val = val;
          this.left = left;
          this.right = right;
      }
  }