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;
  }
};

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