/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
int preorder(struct TreeNode* root,int pre){
if(!root) return 0;
if(!root->left&&!root->right&&pre==1) return root->val;
int leftsum=preorder(root->left,1);
int rightsum=preorder(root->right,-1);
return leftsum+rightsum;
}
int sumOfLeftLeaves(struct TreeNode* root){
return preorder(root,0);
}結果：
