Create 132_pattern.cpp

Author: avidLearnerInProgress

132_pattern.cpp

@@ -0,0 +1,52 @@
+class Solution {
+public:
+    bool find132pattern(vector<int>& nums) {
+        // completely wrong first initial thoughts !!!
+        //how can i apply sliding window??, there's negative bounds defined!
+/*      int size = nums.size();
+        if (size <= 1) return false;
+        
+        int start = 0, end = 1;
+        while(end < size) {
+            if(nums[start] < nums[end]) { //start < end
+                if(end >= size - 1) {
+                    return false;
+                }
+                if(nums[end + 1] < nums[end] and nums[end + 1] < nums[start]) { //next_to_end < end
+                    cout<<nums[start]<<nums[end]<<" "<<nums[end + 1]<<"\n";
+                    return true;
+                }
+            }
+            start++, end++;
+        }
+        return false;
+*/
+    
+        /*
+            nums[k] < nums[j]
+            nums[k] > nums[i]
+            nums[j] > nums[i]
+            
+            finding nums[k] is the problem! This was a bit difficult to figure out - monotonic decreasing sequence.
+        */
+        
+        
+        stack<pair<int, int>> st;
+        int currentMin = nums[0];
+        
+        
+        for(int i = 1; i < nums.size(); ++i) {
+            while(!st.empty() and nums[i] >= st.top().first) {
+                st.pop();
+            }
+            if(!st.empty() and nums[i] < st.top().first and nums[i] > st.top().second) {
+                return true;
+            }
+            
+            st.push({nums[i], currentMin});
+            currentMin = min(currentMin, nums[i]);
+        }
+        return false;
+
+    }
+};