404. Sum of Left Leaves（C语言）

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.

我是看了答案才觉得其实明白了题意，答案也就出来了

求树里面，所有有左孩子，而左孩子没有孩子的这样的左孩子值的和

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     struct TreeNode *left; *     struct TreeNode *right; * }; */int sumOfLeftLeaves(struct TreeNode* root) {    if(root==NULL){        return 0;    }    if(root->left!=NULL&&root->left->left==NULL&&root->left->right==NULL){        return root->left->val+sumOfLeftLeaves(root->right);    }    return sumOfLeftLeaves(root->left)+sumOfLeftLeaves(root->right);}