# 437. Path Sum III

## 1. Question

Given the root of a binary tree and an integer targetSum, return the number of paths where the sum of the values along the path equals targetSum.

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

## 2. Examples

Example 1:

Input: root = [10,5,-3,3,2,null,11,3,-2,null,1], targetSum = 8
Output: 3
Explanation: The paths that sum to 8 are shown.


Example 2:

Input: root = [5,4,8,11,null,13,4,7,2,null,null,5,1], targetSum = 22
Output: 3


## 3. Constraints

• The number of nodes in the tree is in the range [0, 1000].
• -109 <= Node.val <= 109
• -1000 <= targetSum <= 1000

## 5. Solutions

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

private int getCount(TreeNode root, int sum) {
int res = 0;
if (root == null) {
return res;
}
if (root.val == sum) {
res++;
}
return res += getCount(root.left, sum - root.val) + getCount(root.right, sum - root.val);
}
}