Search Range in Binary Search Tree

Given two values k1 and k2 (where k1 < k2) and a root pointer to a Binary Search Tree. Find all the keys of tree in range k1 to k2. i.e. print all x such that k1<=x<=k2 and x is a key of given BST. Return all the keys in ascending order.

Example

For example, if k1 = 10 and k2 = 22, then your function should print 12, 20 and 22.

          20

       /        \

    8           22

  /     \

4       12

class Solution {
    void pushLeft(stack<TreeNode *> &st, TreeNode *root, int k1) {
        while(root) {
            st.push(root);
            if (root->val < k1) break;
            
            root = root->left;
        }
    }
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) {
        stack<TreeNode *> st;
        vector<int> output;
        
        pushLeft(st, root, k1);
        
        while(st.size() > 0) {
            TreeNode *t = st.top();
            st.pop();
            
            if (t->val >= k1 && t->val <= k2)
                output.push_back(t->val);
            
            if (t->val <= k2) 
               pushLeft(st, t->right, k1);
        }
        
        return output;
    }
};