304. 二维区域和检索 - 矩阵不可变

  1. class NumMatrix {
  2.     private int[][] matrix;
  3.     private int rows;
  4.     private int cols;
  6.     public NumMatrix(int[][] matrix) {
  7.         if (matrix ==  null)
  8.             this.matrix = null;
  10.         rows = matrix.length;
  11.         if (rows > 0) {
  12.             cols = matrix[0].length;
  14.             this.matrix = new int[rows][cols];
  16.             for (int  i = 0; i < rows; i++) 
  17.                 for (int j = 0; j < cols; j++) 
  18.                     this.matrix[i][j] = matrix[i][j];
  19.         }
  20.     }
  22.     public int sumRegion(int row1, int col1, int row2, int col2) {
  23.         if (matrix == null || row2 > rows || col2 > cols)
  24.             return 0;
  26.         int sum = 0;
  27.         for (int i = row1; i <= row2; i++) 
  28.             for (int j = col1; j <= col2; j++)
  29.                 sum += matrix[i][j];
  31.         return sum;
  32.     }
  33. }
  35. /**
  36.  * Your NumMatrix object will be instantiated and called as such:
  37.  * NumMatrix obj = new NumMatrix(matrix);
  38.  * int param_1 = obj.sumRegion(row1,col1,row2,col2);
  39.  */