Leetcode 255. Verify Preorder Sequence in Binary Search Tree (Medium) (cpp)

Leetcode 255. Verify Preorder Sequence in Binary Search Tree (Medium) (cpp)

Tag: Tree, Stack

Difficulty: Medium

/*

255. Verify Preorder Sequence in Binary Search Tree (Medium)

Given an array of numbers, verify whether it is the correct preorder traversal sequence of a binary search tree.

You may assume each number in the sequence is unique.

Follow up:
Could you do it using only constant space complexity?

*/
class Solution {
public:
bool verifyPreorder(vector<int>& preorder) {
int i = 0;
verifyPreorder(preorder, i, INT_MIN, INT_MAX);
return i >= preorder.size() ? true : false;
}
private:
void verifyPreorder(vector<int>& nums, int& i, int low, int high) {
if (i >= nums.size() || nums[i] > high || nums[i] < low) return;
int cur = nums[i++];
verifyPreorder(nums, i, low, cur);
verifyPreorder(nums, i, cur, high);
return;
}
};