力扣404. 左叶子之和C++

class Solution {
public:	
int sumOfLeftLeaves(TreeNode* root) {        
	if(root==NULL)return 0;        //判断根结点
	if(root->left==NULL)return sumOfLeftLeaves(root->right);//判断是否存在左子树        
	if(root->left->left==NULL&& root->left->right==NULL)//左子树是叶子结点           
 		return root->left->val+sumOfLeftLeaves(root->right);//向右子树递归
 	return sumOfLeftLeaves(root->left)+sumOfLeftLeaves(root->right);//同时向左右递归
 	}
};