src/main/java/com/fishercoder/solutions/_304.java

package com.fishercoder.solutions;

public class _304 {

    public static class Solution1 {
        public class NumMatrix {

            public NumMatrix(int[][] matrix) {
                if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
                    return;
                }

                /**The dimensions of this tot matrix is actually 1 bigger than the given matrix, cool!*/
                tot = new int[matrix.length + 1][matrix[0].length + 1];
                for (int i = 0; i < matrix.length; i++) {
                    for (int j = 0; j < matrix[0].length; j++) {
                        tot[i + 1][j + 1] =
                                matrix[i][j] + tot[i + 1][j] + tot[i][j + 1] - tot[i][j];
                    }
                }
            }

            public int sumRegion(int row1, int col1, int row2, int col2) {
                return tot[row2 + 1][col2 + 1] - tot[row2 + 1][col1] - tot[row1][col2 + 1]
                        + tot[row1][col1];
            }

            int[][] tot;
        }
    }
/**
 * Your NumMatrix object will be instantiated and called as such:
 * NumMatrix obj = new NumMatrix(matrix);
 * int param_1 = obj.sumRegion(row1,col1,row2,col2);
 */
}