Merge branch 'master' of https://github.com/Arjiit/LeetCode-Patterns

Author: Arjiit

Dynamic Programming/rangeSumQuery2d.java

@@ -0,0 +1,39 @@
+class NumMatrix {
+    /*
+    T.C. for one query is O(1)
+    */
+    private int[][] dp;
+    public NumMatrix(int[][] matrix) {
+        int row = 0;
+        int col = 0;
+        if (matrix.length != 0) {
+            row = matrix.length;
+            col = matrix[0].length;
+        }
+        dp = new int[row+1][col+1];
+        
+        for (int i=1; i<dp.length; i++) {
+            for (int j=1; j<dp[0].length; j++) {
+                // filling up sum of boxes from (0,0) to (i-1,j-1) at dp[i][j]
+                // vertical box value + horizontal box value + current box value of matrix - (value that included twice) 
+                dp[i][j] = dp[i-1][j] + dp[i][j-1] + matrix[i-1][j-1] - dp[i-1][j-1]; 
+            }
+        }
+        
+    }
+    
+    public int sumRegion(int row1, int col1, int row2, int col2) {
+        row1++;
+        row2++;
+        col1++;
+        col2++;
+        
+        return dp[row2][col2] - dp[row1-1][col2] - dp[row2][col1-1] + dp[row1-1][col1-1];
+    }
+}
+
+/**
+ * Your NumMatrix object will be instantiated and called as such:
+ * NumMatrix obj = new NumMatrix(matrix);
+ * int param_1 = obj.sumRegion(row1,col1,row2,col2);
+ */