Merge pull request neetcode-gh#3033 from The-SS/main

Create 0456-132-pattern.cpp

Author: MHamiid

cpp/0456-132-pattern.cpp

@@ -0,0 +1,35 @@
+/*
+    Given nums, return true if there is a 132 pattern where
+    num[i] < nums[k] < nums[j] for i < j < k
+
+    Use a monotonically decreasing stack to store a pair
+    {candidate nums[j], candidate nums[i]} where 
+    candidate nums[i] is the minimum number in nums before j
+
+    Traverse nums.
+    Pop the stack while n >= candidate nums[j] at the top of the stack (n is a better candidate than those)
+    Then, if stack not empty, check if 132 patter if found --> return True
+    Else, add the current num as a candidate nums[j] with the current min as the candidate nums[i] then update current min
+*/
+class Solution {
+public:
+    bool find132pattern(vector<int>& nums) {
+        stack<pair<int, int>> s;
+        int curMin = nums[0];
+
+        for(auto & n : nums){
+            // pop all values in stack that have nums[j] candidate <= n
+            while(!s.empty() && s.top().first <= n){
+                s.pop();
+            }
+            // if stack not empty, check if we found 132 pattern
+            if(!s.empty() && s.top().second < n) return true;
+            else{
+                // add n to stack and update curMin
+                s.push({n, curMin});
+                curMin = min(curMin, n);
+            }
+        }
+        return false;
+    }
+};