LintCode Search Range in Binary Search Tree

/**
* 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
vector<int> seen;
search(root, k1, k2, seen);
return seen;
}

void search(TreeNode* root, int k1, int k2, vector<int>& seen) {
if (k2 < k1 || root == NULL) {
return;
}
if (k1 >= root->val) {
// range all in right tree
if (k1 == root->val) {
seen.push_back(k1);
}
search(root->right, k1, k2, seen);
} else if (k2 <= root->val) {
// range all in left tree
search(root->left, k1, k2, seen);
if (k2 == root->val) {
seen.push_back(k2);
}
} else {
// normal
search(root->left, k1, root->val, seen);
seen.push_back(root->val);
search(root->right, root->val, k2, seen);
}
}
};

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
vector<int> seen;
search(root, k1, k2, seen);
return seen;
}

void search(TreeNode* root, int k1, int k2, vector<int>& seen) {
if (k2 < k1 || root == NULL) {
return;
}
if (k1 < root->val) {
search(root->left, k1, min(root->val, k2), seen);
}
if (k1 <= root->val && root->val <= k2) {
seen.push_back(root->val);
}
if (k2 > root->val) {
search(root->right, max(root->val, k1), k2, seen);
}
}
};