Create 304. Range Sum Query 2D - Immutable

Author: rajatag03

304. Range Sum Query 2D - Immutable

@@ -0,0 +1,31 @@
+class NumMatrix {
+
+    int[][] matrix;
+    public NumMatrix(int[][] matrix) {
+        for(int i=0;i<matrix.length;i++){
+            for(int j=1;j<matrix[0].length;j++){
+                matrix[i][j] += matrix[i][j-1];
+            }
+        }
+        
+        for(int i=1;i<matrix.length;i++){
+            for(int j=0;j<matrix[0].length;j++){
+                matrix[i][j] += matrix[i-1][j];
+            }
+        }
+        
+        this.matrix = matrix;
+    }
+    
+    public int sumRegion(int row1, int col1, int row2, int col2) {
+        int total = matrix[row2][col2];
+        int extra = (col1!=0?matrix[row2][col1-1]:0) + (row1!=0?matrix[row1-1][col2]:0) - ((row1!=0 && col1!=0)?matrix[row1-1][col1-1]:0);
+        return total - extra;
+    }
+}
+
+/**
+ * Your NumMatrix object will be instantiated and called as such:
+ * NumMatrix obj = new NumMatrix(matrix);
+ * int param_1 = obj.sumRegion(row1,col1,row2,col2);
+ */