leetcode508

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    Stack<TreeNode> S = new Stack<TreeNode>();
        private void postNode(TreeNode node)
        {
            if (node != null)
            {
                S.Push(node);//先序遍历，遍历所有节点
                if (node.left != null)
                {
                    postNode(node.left);
                }
                if (node.right != null)
                {
                    postNode(node.right);
                }
            }
        }

        private int sumSubTree(TreeNode node)
        {
            if (node != null)
            {
                var sum = node.val;
                if (node.left != null)
                {
                    sum += sumSubTree(node.left);
                }
                if (node.right != null)
                {
                    sum += sumSubTree(node.right);
                }
                return sum;
            }
            else
            {
                return 0;
            }

        }

        public int[] FindFrequentTreeSum(TreeNode root)
        {
            if (root == null)
            {
                return new int[] { };
            }
            postNode(root);
            var list = S.ToList();
            Dictionary<int, int> dic = new Dictionary<int, int>();//key是sum值，value是次数
            foreach (var l in list)
            {
                var sum = sumSubTree(l);
                if (!dic.ContainsKey(sum))
                {
                    dic.Add(sum, 1);
                }
                else
                {
                    dic[sum]++;
                }
            }

            var result = dic.OrderByDescending(x => x.Value).ToList();

            var max = int.MinValue;
            var arylist = new List<int>();
            foreach (var r in result)
            {
                var count = r.Value;
                var cur = r.Key;
                if (count >= max)
                {
                    max = count;
                    arylist.Add(cur);
                }
                else
                {
                    break;
                }
            }

            var ary = arylist.ToArray();
            return ary;
        }
}

https://leetcode.com/problems/most-frequent-subtree-sum/#/description