class Solution {
public:
void helper(TreeNode* root,int& sum,bool is_left){
if(root==NULL){//空节点返回
return;
}
//为叶子结点
if(root->left==NULL&&root->right==NULL){
if(is_left){//为左结点
sum+=root->val;
}
return;
}
helper(root->left,sum,true);//遍历左子树,标识是左子树
helper(root->right,sum,false);//遍历右子树,标识不是左子树
}
int sumOfLeftLeaves(TreeNode* root) {
//处理特殊的情形
if(root==NULL||(root->left==NULL&&root->right==NULL)){
return 0;
}
int sum=0;
helper(root,sum,true);
return sum;
}
};