2023-09-30 Daily Challenge

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In: DailyChallenge
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Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 30

Description

132 Pattern

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

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  bool find132pattern(vector<int>& nums) {
    if(nums.size() < 3) return false;
    stack<int> three;
    int two = INT_MIN;
    three.push(nums.back());
    for(int i = nums.size()-1; i >=0 ; --i) {
      if(nums[i] < two) return true;
      while(three.size() && three.top() < nums[i]) {
        two = three.top();
        three.pop();
      }
      three.push(nums[i]);
    }
    return false;
  }
};

// Accepted
// 103/103 cases passed (49 ms)
// Your runtime beats 98.35 % of cpp submissions
// Your memory usage beats 85.68 % of cpp submissions (48 MB)
Algorithm