404、左叶子之和

题目链接：

递归

class Solution {
public:    
    int sumOfLeftLeaves(TreeNode* root) {
        int ans = 0;
        if (!root) return 0;
        
        if (root->left) {
            if ((!root->left->left) && (!root->left->right)) {
                ans += root->left->val;
            }
        }
        
        ans += sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);//
        return ans;//这里一开始写成了return sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right) QAQ
    }
};
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