404. 左叶子之和c

/**
 * 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：