LeetCode 304. 二维区域和检索 - 矩阵不可变

解题思路

套模板

相关代码

class NumMatrix {
    int a[][] = new int[210][210];
    int s[][] = new int[210][210];
    int m,n;
    public NumMatrix(int[][] matrix) {
        for(int i=0;i<matrix.length;i++){
            for(int j=0;j<matrix[0].length;j++){
                a[i+1][j+1] = matrix[i][j];
            }
        }
        //m表示行,n表示列
        m = matrix.length;
        n = matrix[0].length;

        for(int i=1;i<=matrix.length;i++)
            for(int j=1;j<=matrix[0].length;j++)
                s[i][j] = s[i][j-1]+s[i-1][j]-s[i-1][j-1]+a[i][j];
    }
    
    public int sumRegion(int row1, int col1, int row2, int col2) {
return s[row2+1][col2+1]-s[row2+1][col1]-s[row1][col2+1]+s[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);
 */