/**
 * 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:
    
    bool isLeave(TreeNode* root) {
        if (!root) return false;
        if (!root->left && !root->right) return true;
        return false;
    }
    
    int sumOfLeftLeaves(TreeNode* root) {
        if (isLeave(root)) return 0;
        return sumOfLeftLeaves_(root);
    }
    
    int sumOfLeftLeaves_(TreeNode* root) {
        if (!root) return 0;
        if (isLeave(root)) return root->val;
        return sumOfLeftLeaves_(root->left) +  ( isLeave(root->right) ? 0 : sumOfLeftLeaves_(root->right) ) ;
    }
};