user69514 - 6 months ago 28

Java Question

I have a two dimensional array that I need to rotate 90 degrees clockwise, however I keep getting arrayindexoutofbounds...

`public int[][] rorateArray(int[][] arr){`

//first change the dimensions vertical length for horizontal length

//and viceversa

int[][] newArray = new int[arr[0].length][arr.length];

//invert values 90 degrees clockwise by starting from button of

//array to top and from left to right

int ii = 0;

int jj = 0;

for(int i=0; i<arr[0].length; i++){

for(int j=arr.length-1; j>=0; j--){

newArray[ii][jj] = arr[i][j];

jj++;

}

ii++;

}

return newArray;

}

Answer

I don't understand your loops' logic -- shouldn't it be

```
for(int i=0; i<arr[0].length; i++){
for(int j=arr.length-1; j>=0; j--){
newArray[i][j] = arr[j][i];
}
}
```

Net of whether each index goes up, like `i`

here, or down, like `j`

here (and of whether either or both need to be "flipped" in the assignment, e.g using `arr.length-1-j`

in lieu of plain `j`

on one side of the `=`

in the assignment;-), since `arr`

dimensions are `arr.length`

by `arr[0].length`

, and vice versa for `newArray`

, it seems to me that the first index on `arr`

(second on `newArray`

) must be the one spanning the range from 0 to `arr.length-1`

included, and the other range for the other index.

This is a kind of "basic dimensional analysis" (except that "dimension" is used in a different sense than normally goes with "dimensional analysis" which refers to physical dimensions, i.e., time, mass, length, &c;-). The issue of "flipping" and having each loop go up or down depend on visualizing exactly what you mean and I'm not the greatest "mental visualizer" so I think, in real life, I'd try the various variants of this "axis transposition" until I hit the one that's meant;-).