题意:统计左叶子节点的和。
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: bool leftleaf(TreeNode *root){ if(root == NULL) return false; return root -> left == NULL && root -> right == NULL; } int sumOfLeftLeaves(TreeNode* root) { if(root == NULL) return 0; if(leftleaf(root -> left)) return root -> left -> val + sumOfLeftLeaves(root -> right); else return sumOfLeftLeaves(root -> left) + sumOfLeftLeaves(root -> right); } };