Solution to Leetcode 404 Sum of Left Leaves

Problem Description could be found @https://leetcode.com/problems/sum-of-left-leaves/

Solution

class Solution {

public:
    int helper(TreeNode* root, TreeNode *parent){
        if (root->left == NULL && root->right  == NULL && root == parent->left ){
            return root->val;
        }
       
        int rightVal = 0;
        int leftVal = 0;
       
        if (root->left != NULL)
            leftVal = helper(root->left, root);
     
       if ( root->right != NULL)
            rightVal = helper(root->right, root);
       
        return (leftVal + rightVal);
    }
    int sumOfLeftLeaves(TreeNode* root) {
        if (root == NULL )
            return 0;
        if (root->left == NULL && root->right == NULL)
            return 0;
           
     
        int num = helper(root, NULL);
        return num;
     
    }
};