404. Sum of Left Leaves

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

Example:

    3   / \  9  20    /  \   15   7There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

LeetCode AC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 == NULL) return 0;        if (root->left && root->left->left == NULL && root->left->right == NULL)             return root->left->val + sumOfLeftLeaves(root->right);        return sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);    }};