树第3天

第3天

652. 寻找重复的子树

class Solution {
    Map<String, Integer> map = new HashMap<>();
    List<TreeNode> res = new ArrayList<>();
    public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
        traverse(root);
        return res;
    }

    String traverse(TreeNode root){
        if(root == null)
            return "#";
        
        String left = traverse(root.left);
        String right = traverse(root.right);

        String treStr = left + "," + right + "," + root.val;
        int i = map.getOrDefault(treStr, 0);
        if(i == 1)
            res.add(root);
        map.put(treStr, i + 1);
        return treStr;
    }
}