【LeetCode刷题-哈希】--652.寻找重复的子树

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652.寻找重复的子树

/*** Definition for a binary tree node.* public 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;*     }* }*/
class Solution {Map<String,TreeNode> treeMap = new HashMap<>();Set<String> keySet = new HashSet<>();public List<TreeNode> findDuplicateSubtrees(TreeNode root) {visitTreeNode(root);return new ArrayList<>(treeMap.values());}private String visitTreeNode(TreeNode node){if(node == null){return "";}//将节点的value和它的左子树和右子树节点拼接起来作为keyString treeNodeKey = node.val+"(" + visitTreeNode(node.left)+","+visitTreeNode(node.right)+")";if(!keySet.add(treeNodeKey)){treeMap.put(treeNodeKey,node);}return treeNodeKey;}
}

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