Search Range in Binary Search Tree

递归遍历即可，root为空时，返回result并没有什么作用，因为我们并不用它，返回它只是因为函数需要一个返回值。

/** * Definition of TreeNode: * class TreeNode { * public: *     int val; *     TreeNode *left, *right; *     TreeNode(int val) { *         this->val = val; *         this->left = this->right = NULL; *     } * } */class Solution {public:    /**     * @param root: The root of the binary search tree.     * @param k1 and k2: range k1 to k2.     * @return: Return all keys that k1<=key<=k2 in ascending order.     */    vector<int> searchRange(TreeNode* root, int k1, int k2) {        // write your code here        if(root==nullptr)return result;        searchRange(root->left,k1,k2);        if(root->val>=k1&&root->val<=k2)result.push_back(root->val);        searchRange(root->right,k1,k2);        return result;                            }private:   vector<int> result;};