Update MaximumSumSubMatrixInAGivenMatrix.java

Author: 17tanya

DynamicProgramming/MaximumSumSubMatrixInAGivenMatrix.java

@@ -7,5 +7,82 @@
 
 */
 
+class Point{
+    int x;
+    int y;
+    
+    Point(int i, int j){
+        x = i;
+        y = j;
+    }
+    
+}
+
+class SubMatrix{
+    int sum[][];
+    
+    public void fillSumMatrix(int A[][]){
+        int n = A.length;
+        int m = A[0].length;
+        
+        sum = new int[n][m];
+        
+        sum[0][0] = A[0][0];
+        
+        //pre-process first row
+        for(int j=1 ; j < m ; j++){
+            sum[0][j] = sum[0][j-1] + A[0][j];
+        }
+        
+        //pre-process first col
+        for(int i=1 ; i < n ; i++){
+            sum[i][0] = sum[i-1][0] + A[i][0];
+        }
+        
+        //compute rest of the sum-matrix
+        for(int i=1 ; i < n ; i++){
+            for(int j=1 ; j < m ; j++){
+                sum[i][j] = A[i][j] + sum[i-1][j] + sum[i][j-1] - sum[i-1][j-1];
+            }
+        }
+    }
+    
+    public Point maxSumSubmatrix(int k){ //returns the bottom right corner of the maximum sum submatrix
+        //dimensions of the required submatrix --> (k*k)
+        
+        //dimensions of main matrix
+        int n = sum.length;
+        int m = sum[0].length;
+        
+        int currSum = 0;
+        int maxSum = 0;
+        Point p = null;
+        
+        for(int i=k-1 ; i < n ; i++){
+            for(int j=k-1 ; j < m ; j++){
+                
+                currSum = sum[i][j];
+                
+                if(i-k >= 0){
+                    result -= sum[i-k][j];
+                }
+                if(j-k >= 0){
+                    result -= sum[i][j-k];
+                }
+                if(i-k >= 0 && j-k >= 0){
+                    result += sum[i-k][j-k];
+                }
+                
+                if(maxSum < currSum){
+                    maxSum = currSum;
+                    p = new Point(i,j);
+                }
+            }
+        }
+        return p;
+        
+    }
+    
+}