find duplicate trees.txt

/**
 * 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 {
    int t;
    Map<String, Integer> trees;
    Map<Integer, Integer> count;
    List<TreeNode> ans;
    public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
        t=1;
        trees=new HashMap();
        count =new HashMap();
        ans=new ArrayList();
        lookup(root);
        return ans;
    }
    public int lookup(TreeNode node)
    {
        if(node==null)
            return 0;
        String serial = node.val+","+lookup(node.left)+","+lookup(node.right);
        int uid=trees.computeIfAbsent(serial,x-> t++);
        count.put(uid, count.getOrDefault(uid,0) + 1);
        if(count.get(uid)==2)
            ans.add(node);
        return uid;
    }
    
}