题干：

代码;

class Solution {
public:
    bool traversal(TreeNode* node, int count){
        if(node == NULL)return false;

        if(!node -> left && !node -> right && count == 0)return true;
        if(!node -> left && !node -> right && count != 0)return false;

        if(node -> left){
            count -= node -> left -> val;
            if(traversal(node -> left, count))return true;
            count += node -> left -> val;
        }
        if(node -> right){
            count -= node -> right -> val;
            if(traversal(node -> right, count))return true;
            count += node -> right -> val;
        }

        return false;
    }
    bool hasPathSum(TreeNode* root, int targetSum) {
        if(root == NULL)return false;
        return traversal(root, targetSum - root -> val);
    }
};

注意count是从父节点开始减的，因为需要不断递归下去所以必须显示出方向，也即node -> left -> val。

另外必须判断root == NULL 情况，不管是在递归函数中还是在主函数中。

类似题：

代码：

class Solution {
private:
    void traversal(TreeNode* node, int count, vector<int> tmp, vector<vector<int>> &res){
        if(node == NULL)return;
        if(!node -> left && !node -> right && count == 0)res.push_back(tmp);
        if(!node -> left && !node -> right && count != 0)return;

        if(node -> left){
            tmp.push_back(node -> left -> val);
            count -= node -> left -> val;
            traversal(node -> left, count, tmp, res);
            count += node -> left -> val;
            tmp.pop_back();
        }
        if(node -> right){
            tmp.push_back(node -> right -> val);
            count -= node -> right -> val;
            traversal(node -> right, count, tmp, res);
            count += node -> right -> val;
            tmp.pop_back();
        }
        return;
    }
public:
    vector<vector<int>> pathSum(TreeNode* root, int targetSum) {
        vector<int> tmp;
        vector<vector<int>> res;
        if(root == NULL)return res;
        tmp.push_back(root -> val);
        traversal(root, targetSum - root -> val, tmp, res);
        return res;
    }
};

注意，需要在调用前先将根节点值传入tmp内，以及在调用时传入sum - root - > val。