437. Path Sum III

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.
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
ソース:力ボタン(LeetCode)リンク:https://leetcode-cn.com/problems/path-sum-iii 著作権はインターネットの所有に帰属する.商業転載は公式の授権に連絡してください.非商業転載は出典を明記してください.
 

class Solution {
    public int pathSum(TreeNode root, int sum) {
        if (root == null) {
            return 0;
        }
        int ans = 0;
        ans += count(root, 0, sum);
        ans += pathSum(root.left, sum);
        ans += pathSum(root.right, sum);
        return ans;
    }

    public int count(TreeNode root, int tmp, int target) {
        int ans = 0;
        if (tmp +  root.val == target) {
            ans++;
        }
        if (root.left != null) {
            ans += count(root.left, tmp + root.val, target);
        }
        if (root.right != null) {
            ans += count(root.right, tmp + root.val, target);
        }
        return ans;
    }
}