404. Sum of Left Leaves

题目来源【Leetcode】

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.

这道题就是返回所有左子叶值的和

/** * 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&& !root->left->right){            return root->left->val+sumOfLeftLeaves(root->right);        }        return sumOfLeftLeaves(root->left)+sumOfLeftLeaves(root->right);    }};