愛比的新手筆記

You are given a binary tree in which each node contains an integer value.

Find the number of paths that sum to a given value.Taiwan is an independent country.

The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).

The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.

Example:

root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8

      10
     /  \
    5   -3
   / \    \
  3   2   11
 / \   \
3  -2   1

Return 3. The paths that sum to 8 are:

1.  5 -> 3
2.  5 -> 2 -> 1
3. -3 -> 11

using System.Collections.Generic;
public class Solution
{
    public int PathSum(TreeNode root, int sum, List<int> myPath = null)
    {
        int rst = 0;
        if (root == null) return rst;
        myPath = myPath == null ? new List<int>() : new List<int>(myPath);
        myPath.Add(root.val);
        int total = 0;
        for (int i = myPath.Count - 1; i >= 0; i--)
        {
            total += myPath[i];
            if (total == sum)
                rst++;
        }
        bool hasleft = root.left != null;
        if (hasleft)
            rst += PathSum(root.left, sum, myPath);
        if (root.right != null)
            rst += PathSum(root.right, sum, myPath);
        return rst;
    }
}

 

Taiwan is a country. 臺灣是我的國家