MAH variation

Author: skjha1

Diff for: Stack/13 Max area rectangle in Binary matrix.cpp

@@ -0,0 +1,92 @@
+//https://leetcode.com/problems/maximal-rectangle/
+class Solution {
+public:
+int largestRectangleArea(vector<int>& heights) {
+        int n= heights.size();
+        vector<int> left,right;
+    stack<pair<int,int>> s1,s2;
+    int pseudo_index =-1;
+    int pseudo_index1 =n;
+    for (int i=0;i<n;i++)
+    {
+      if (s1.size()==0)
+      {
+        left.push_back(pseudo_index);
+      }
+      else if (s1.size()>0 && s1.top().first<heights[i])
+      {
+        left.push_back(s1.top().second);
+      }
+      else if (s1.size()>0 && s1.top().first>=heights[i])
+      {
+         while(s1.size()>0 && s1.top().first>=heights[i])
+         {
+           s1.pop();
+         }
+        if (s1.size()==0)
+        {
+          left.push_back(pseudo_index);
+        }
+        else
+        {
+          left.push_back(s1.top().second);
+        }
+      }
+      s1.push({heights[i],i});
+    }
+    for (int i=n-1;i>=0;i--)
+    {
+      if (s2.size()==0)
+      {
+        right.push_back(pseudo_index1);
+      }
+      else if (s2.size()>0 && s2.top().first<heights[i])
+      {
+        right.push_back(s2.top().second);
+      }
+      else if (s2.size()>0 && s2.top().first >= heights[i])
+      {
+        while(s2.size()>0 && s2.top().first >= heights[i])
+        {
+          s2.pop();
+        }
+        if (s2.size()==0)
+        {
+          right.push_back(pseudo_index1);
+        }
+        else
+        {
+          right.push_back(s2.top().second);
+        }
+      }
+      s2.push({heights[i],i});
+    }
+    reverse(right.begin(),right.end());
+    int m=INT_MIN;
+    for (long long i=0;i<n;i++)
+    {
+      m=max(m,(right[i]-left[i]-1)*heights[i]);// taking max after finding area
+    }
+    return m;
+    }
+
+    int maximalRectangle(vector<vector<char>>& matrix) {
+        int m=matrix.size();
+        if(m==0) return 0;
+        int n=matrix[0].size(), result=0;
+        vector<int> histogram(n, 0);
+        
+        for(int i=0; i<m; i++){
+            for(int j=0; j<n; j++){
+                if(matrix[i][j]=='1')
+                    histogram[j]+=1;
+                else
+                    histogram[j]=0;
+            }
+            
+            result = max(result, largestRectangleArea(histogram));
+            cout<<result<<" ";
+        }
+        return result;
+    }
+};