#Leetcode# 404. Sum of Left Leaves

https://leetcode.com/problems/sum-of-left-leaves/

Find the sum of all left leaves in a given binary tree.

Example:

    3
   / 
  9  20
    /  
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

代码：

/**
 * 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 sumOfLeftLeaves(TreeNode* root) {
        if(!root) return 0;
        int sum = 0;
        if(root -> left && !root -> left -> left && !root -> left -> right)
            sum = root -> left -> val;
        sum += sumOfLeftLeaves(root -> left) + sumOfLeftLeaves(root -> right);
        return sum;
    }
};