[Leetcode] 652. Find Duplicate Subtrees

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:

        1
       / \
      2   3
     /   / \
    4   2   4
       /
      4

The following are two duplicate subtrees:

      2
     /
    4

and

    4

Therefore, you need to return above trees' root in the form of a list.

------------------------------------------------------------

找出重複的樹

 

class Program
    {
        static void Main(string[] args)
        {

            //[0,0,0,0,null,null,0,null,null,null,0]
            Solution solution = new Solution();

            //TreeNode root = new TreeNode(0);
            //root.left = new TreeNode(0);
            //root.right = new TreeNode(0);
            //root.left.left = new TreeNode(0);

            //root.right.right = new TreeNode(0);
            //root.right.right.right = new TreeNode(0);


            TreeNode root = new TreeNode(1);
            root.left = new TreeNode(2);
            root.left.left = new TreeNode(4);
            root.right = new TreeNode(3);
            root.right.left = new TreeNode(2);
            root.right.right = new TreeNode(4);
            root.right.left.left = new TreeNode(4);

            var result = solution.FindDuplicateSubtrees(root);
            Console.ReadLine();
        }
    }


    public class TreeNode
    {
        public int val;
        public TreeNode left;
        public TreeNode right;
        public TreeNode(int x) { val = x; }
    }

    public class Solution
    {
        public IList<TreeNode> FindDuplicateSubtrees(TreeNode root)
        {
            Dictionary<string, int> duplicated = new Dictionary<string, int>();

            List<TreeNode> result = new List<TreeNode>();
            var sss = TreeTraverse(root, ref result, ref duplicated);
            return result;
        }

        public string TreeTraverse(TreeNode root, ref List<TreeNode> result, ref Dictionary<string, int> duplicated)
        {
            if (root == null)
                return "";
            List<string> temp = new List<string>();
            if (root != null) temp.Add(root.val.ToString());

            string leftTree = TreeTraverse(root.left, ref result, ref duplicated);
            temp.Add(leftTree);

            string rightTree = TreeTraverse(root.right, ref result, ref duplicated);
            temp.Add(rightTree);

            //根,左子樹,右子樹會形成key,value則為次數
            var treeList = string.Join(",", temp);
            if (false == string.IsNullOrEmpty(treeList))
            {
                if (duplicated.ContainsKey(treeList))
                    duplicated[treeList]++;
                else
                    duplicated.Add(treeList, 1);
                //發現重複就加入結果集內
                if (duplicated[treeList] == 2) result.Add(root);
            }


            return treeList;
        }
    }