Merge pull request neetcode-gh#3164 from KaiyangYao/main

Create: 0304-range-sum-query-2d-immutable.java

Author: sujal-goswami

java/0304-range-sum-query-2d-immutable.java

@@ -0,0 +1,25 @@
+class NumMatrix {
+    int[][] preSum;
+
+    public NumMatrix(int[][] matrix) {
+        int m = matrix.length;
+        int n = matrix[0].length;
+        preSum = new int[m + 1][n + 1];
+
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                preSum[i + 1][j + 1] = preSum[i + 1][j] + preSum[i][j + 1] - preSum[i][j] + matrix[i][j]; 
+            }
+        }
+    }
+    
+    public int sumRegion(int row1, int col1, int row2, int col2) {
+        return preSum[row2 + 1][col2 + 1] - preSum[row2 + 1][col1] - preSum[row1][col2 + 1] + preSum[row1][col1];
+    }
+}
+
+/**
+ * Your NumMatrix object will be instantiated and called as such:
+ * NumMatrix obj = new NumMatrix(matrix);
+ * int param_1 = obj.sumRegion(row1,col1,row2,col2);
+ */