Leetcode 437. Path Sum III (Easy) (cpp)

Leetcode 437. Path Sum III (Easy) (cpp)

Tag: Tree

Difficulty: Easy

/*

437. Path Sum III (Easy)

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

*/
/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
	int pathSum(TreeNode* root, int sum) {
		unordered_map<int, int> mapping;
		mapping[0] = 1;
		return pathSum(root, 0, sum, mapping);
	}
private:
	int pathSum(TreeNode* root, int sum, const int& target, unordered_map<int, int>& mapping) {
		if (root == NULL) {
			return 0;
		}
		sum += root->val;
		int res = mapping.find(sum - target) != mapping.end() ? mapping[sum - target] : 0;
		mapping[sum]++;
		res += pathSum(root->left, sum, target, mapping) + pathSum(root->right, sum, target, mapping);
		mapping[sum]--;
		return res;
	}
};