Leetcode 437. Path Sum III

通过cnt进行计数，然后进行递归找。在递归的过程中，只要sum为0，则cnt加一

/**
 * 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 cnt = 0;
    int pathSum(TreeNode* root, int sum) {
        if(!root) return 0;
        getSum(root, sum);
        pathSum(root->left, sum);
        pathSum(root->right, sum);
        return cnt;
    }
    void getSum(TreeNode* root, int sum) {
        if(!root) return;
        sum -= root->val;
        if(sum == 0) cnt++;
        getSum(root->left, sum);
        getSum(root->right, sum); 
    }
};