456. 132 Pattern | LeetCode Solution

 456. 132 Pattern | LeetCode Solution

Given an array of n integers nums, a 132 pattern is a subsequence of three integers nums[i], nums[j] and nums[k] such that i < j < k and nums[i] < nums[k] < nums[j].

Return true if there is a 132 pattern in nums, otherwise, return false.

 

Example 1:

Input: nums = [1,2,3,4]
Output: false
Explanation: There is no 132 pattern in the sequence.

Example 2:

Input: nums = [3,1,4,2]
Output: true
Explanation: There is a 132 pattern in the sequence: [1, 4, 2].

Example 3:

Input: nums = [-1,3,2,0]
Output: true
Explanation: There are three 132 patterns in the sequence: [-1, 3, 2], [-1, 3, 0] and [-1, 2, 0].

 

Constraints:

• n == nums.length
• 1 <= n <= 2 * 105
• -109 <= nums[i] <= 109

class Solution

{

public:

  bool find132pattern(vector<int> &nums)

  {

    int s3 = INT_MIN;

    stack<int> st;

    for (int i = nums.size() - 1; i >= 0; i--)

    {

      if (nums[i] < s3)

        return true;

      while (!st.empty() && nums[i] > st.top())

      {

        s3 = st.top();

        st.pop();

      }

      st.push(nums[i]);

    }

    return false;

  }

};