借鉴别人的。
class Solution {
public:
int cnt = 0;
int pathSum(TreeNode* root, int sum) {
if (!root)
return 0;
dfs(root, sum);
pathSum(root->left, sum);
pathSum(root->right, sum);
return cnt;
}
void dfs(TreeNode *root, int sum)
{
if (!root)
return;
sum -= root->val;
if (sum == 0)
cnt++;
dfs(root->left, sum);
dfs(root->right, sum);
}
};