Bubble sort on 2D Array Java

问题:

String[][] 2dArray = new String[counter][2];
2dArray [counter][column1] = String.valueOf(counter);
2dArray [counter][column2] = "something something something";
for(int i = 0; i < 2dArray.length-1; i++){
     for(int j = i + 1; j > 0; j--){
       if(2dArray[i][j] < 2dArray[i-1][j]){ 
           int[][] temp = 2dArray[i-1][j];
           2dArray[i-1][j] = 2dArray[i][j];
           2dArray[i][j] = temp;                  
       }
     }
}

Attempting to sort the array so that column 1 is ascending. I've studied the other references on here and mimic'd them but for some reason my IDE does not like the above...

回答1:

If I understand you correctly, I would suggest the following:

What you would need to do is to compare the Integer values of the array:

if(Integer.valueOf(2dArray[i][0]) < Integer.valueOf(2dArray[i-1][0])){

The reason you don't include j is because you are only sorting by the value of the first column. 2dArray[i][0] gets you the value of your counter at that particular row.

I've also seen some other stuff in your code that could use fixing:

for(int i = 0; i < 2dArray.length; i++){
  for(int j = i; j < 2dArray.length; j++){
    if(Integer.valueOf(2dArray[j][0]) > Integer.valueOf(2dArray[j+1][0])){
       String temp[] = 2dArray[j+1];
       2dArray[j+1] = 2dArray[j];
       2dArray[j] = temp;                  
    }
  }
}

This is more in line with what I think is the classic implementation of BubbleSort:

private static void bubblesort(Integer[] array) {
    for (int i = 0; i < array.length; i++) {
        for(int j = 0; j < array.length - 1; j++) {
            if(array[j].compareTo(array[j+1]) > 0) {
                swap(j, j+1, array);
            }
        }
    }

}

private static void swap(Integer index1, Integer index2, Integer[] array) {
    if(index1 == index2)return;
    Integer temp = new Integer(array[index2]);
    array[index2] = array[index1];
    array[index1] = temp;

}

Except in your case, I'm treating your array as a one-dimensional, since you are only sorting by one dimension.

回答2:

If 2dArray is a two dimensional String array like

String[][] 2dArray

then the two strings can be compared using

if(2dArray[i][j].compareTo(2dArray[i-1][j]) > 0)

回答3:

Would this also fix it ?

for (int i = 0; i < 2dArray.length-1; i++){

          for(int j = 0; j < 2dArray.length-1; j++){

              if(2dArray[j][0].compareTo(2dArray[j+1][0])>0){

                String[] temp = 2dArray[j];
                2dArray[j] = 2dArray[j+1];
                2dArray[j+1] = temp;                  
              }
          }
        }

回答4:

for(int i=0;i<2dArray.length-2;i++){
    for(int j=0;j<2dArray[i].length-1;j++){
            if(2dArray[i][j]>2dArray[i+1][j]){
                int temp=2dArray[i][j];
                2dArray[i][j]=2dArray[i+1][j];
                2dArray[i+1][j]=temp;
            }
    }
}

回答5:

char[][] temp = 2dArray[i-1][j];

Your IDE doesn't like you (120%) when you put a char/int/... (per first response) into a two dimension char array.