Question

所以我的问题是，我不能像在单个变量数组中那样切换二维数组的元素。而不是切换元素，他们只是不断重写......

for (int column = 0; column < m[0].length; column++) {
    shufcol = (int)(Math.random()*4);
    temp = column;
    System.out.println(shufcol);

    for(int row = 0; row < m.length; row++) {
        temp = row;
        m[row][temp]=m[row][column];
        m[row][column]= m[row][shufcol];
        m[row][temp] = m[row][shufcol];
    }
}

输入数组（3X4） {{0 1 2 3} {1 4 5 6} {0 7 8 9}}

输出数组 {{2 2 3 2} {5 5 6 5} {8 8 9 8}}

如果您对math.random感到好奇，那就是生成0到3之间的随机列来切换。问题是为什么它只是重写元素而不是切换元素？

Answer 1

我不完全明白你最终想要达到的目标（因为你还没有被告知），但我想，如果你重读这段代码：

temp = row;
m[row][temp]=m[row][column];
m[row][column]= m[row][shufcol];
m[row][temp] = m[row][shufcol];

多次尝试用纸和笔执行它你会发现错误。

Answer 2

如果我理解，这将切换列和shufcol中所有行的值（我没有测试它）：

for (int column = 0; column < m[0].length; column++) {
    shufcol = (int)(Math.random()*4);
    System.out.println(shufcol);

    for(int row = 0; row < m.length; row++) {
        temp = m[row][shufcol];
        m[row][shufcol] = m[row][column];
        m[row][column] = temp;
    }
}

Answer 3

这会切换行内的元素：

  foreach ($request['array'] as $key => $value) {

    if(DB::table('users')->where('id',$value)->where('auth',0)->exists() == true){
       DB::table('users')->where('id', $value)->update(['auth_teacher' => 1]);
    }

  }

输出：

    //input array (3X4) {{0 1 2 3} {1 4 5 6} {0 7 8 9}}
    int[][] m = {{0, 1, 2, 3}, {1, 4, 5, 6}, {0, 7, 8, 9}};


    for (int column = 0; column < m[0].length; column++) {
        int shufcol = (int)(Math.random()*4);
        int shufrow = (int)(Math.random()*3); //need row to switch with, too
        for(int row = 0; row < m.length; row++) {
            if(row == shufrow){
                int tempField =m[row][column];
                m[row][column]= m[row][shufcol];
                m[row][shufcol] = tempField;
                System.out.println("In row " + row + " : column " + column + " was switched with column " + shufcol + "!");
                break; //just switch once per row, easier debugging ^^-d
            }
        }
    }

    //print output array
    for(int row = 0; row < m.length; row++) {
        String line = "\n";
        for (int column = 0; column < m[0].length; column++) {
            line += m[row][column] + " ";
        }
        System.out.print(line);
    }

由于我不完全确定你想做什么，这里是随机切换整个数组中的元素：

In row 2 : column 0 was switched with column 2!
In row 0 : column 1 was switched with column 2!
In row 1 : column 2 was switched with column 3!
In row 0 : column 3 was switched with column 2!

0 2 3 1 
1 4 6 5 
8 7 0 9

产生以下输出：

    //input array (3X4) {{0 1 2 3} {1 4 5 6} {0 7 8 9}}
    int[][] m = {{0, 1, 2, 3}, {1, 4, 5, 6}, {0, 7, 8, 9}};

    for (int column = 0; column < m[0].length; column++) {
        int shufcol = (int)(Math.random()*4);
        int shufrow = (int)(Math.random()*3); //need row to switch with, too
        //there is no point in duplicating the count variable of a loop!
        System.out.println(shufcol);

        for(int row = 0; row < m.length; row++) {
            //check that random field is not current field!
            if(row != shufrow && column != shufcol){
                //switch current with random
                int temp = m[row][column]; // le backuppe
                m[row][column] = m[shufrow][shufcol]; // write le new value of "random source field" to current field
                m[shufrow][shufcol] = temp; // write value of current field to "random source field"
                System.out.println("switched [" + row + "][" + column + "] with [" + shufrow + "]["+ shufcol + "]");
                break; // use break to switch only once per row, easier debugging ^^-d
            }
            else {
                System.out.println("will not switch with self!");
            }

        }
    }

    //print output array
    for(int row = 0; row < m.length; row++) {
        String line = "\n";
        for (int column = 0; column < m[0].length; column++) {
            line += m[row][column] + " ";
        }
        System.out.print(line);
    }

希望这有帮助！ ^^ - d

切换2d阵列的列

3 个答案: