Create 85. Maximal Rectangle (#456)

Author: Chayandas07

85. Maximal Rectangle

@@ -0,0 +1,36 @@
+class Solution {
+public:
+    int maximalRectangle(vector<vector<char>>& matrix) {
+        int maxArea = 0;
+        
+        if(matrix.size() == 0 || matrix[0].size() == 0) return 0;
+        int cols = matrix[0].size();
+        int rows = matrix.size();
+        vector<int>histogram(cols+1, 0);
+        histogram[cols] = -1;
+        stack<pair<int,int>>monotonic;
+        
+        for(auto row: matrix) {
+            for(int i = 0; i < cols; i++) {
+                if(row[i] == '1') {
+                    histogram[i]++;
+                } else {
+                    histogram[i] = 0;
+                } 
+            }
+            
+            for(int i = 0; i < cols+1; i++) {
+                int x = 0;
+                while(!monotonic.empty() && monotonic.top().first >= histogram[i]) {
+                    auto tp = monotonic.top();  monotonic.pop();
+                    int h = tp.first, steps = tp.second;
+                    x += steps;
+                    maxArea = max(maxArea, h*x);
+                }
+                monotonic.push({histogram[i], x+1});
+            }
+        }
+        
+        return maxArea;
+    }
+};