java- "-1" position

I have this question:

The method accepts an integer array as its input and returns a new array which is a permutation of the input array. The method fix34 rearranges the input array such that every 3 is immediately followed by a 4 (e.g. if there is a 3 at position i, there will be a 4 at position i+1). The method keeps the original positions of the 3s but may move any other number, moving the minimal amount of numbers. Assumptions regarding the input:

• The array contains the same number of 3's and 4's (for every 3 there is a 4)
• There are no two consecutive 3s in the array
• The matching 4 for a 3 at some position i is at position j where j > i

ok, so this is what I wrote:

public class Fix34 {

public static void main(String[] args){
    int [] args1 ={3,1,2,3,5,4,4};
    int[] args11=fix34(args1);
    for (int i = 0; i<=args11.length-1;i++ ){
        System.out.print(args11[i]+" ");}}




public static int pos (int[] arr){
    int i= arr.length-1;
    while (arr[i]!=4){
        i=-1;
        }
    return i;
}


public static int[] fix34(int[] nums){
    for(int i = 0; i<=nums.length-1; i++){
        if (nums[i] == 3){
            nums[pos(nums)]=nums[i+1];
            nums[i+1]=4;

        }

    }
    return nums;
}

}

when I insert arrays such {3,2,1,开发者_如何转开发4} it works, but with the array as written in the code, it gives me the error message:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
    at Fix34.pos(Fix34.java:15)
    at Fix34.fix34(Fix34.java:25)
    at Fix34.main(Fix34.java:6)

how come the arrays gets to -1 position?!

Thanks

you are setting it to -1 here:

i=-1;

Your issue in in this piece of code

public static int pos (int[] arr){
    int i= arr.length-1;
    while (arr[i]!=4){
        i=-1;
    }
    return i;
}

If the last element in the array is 4 the while loop is never entered so arrays like 3, 1, 2, 4 are fine. Otherwise the loop is entered and i is set to -1. I think that you mean to decrement. In that case replace

i=-1

with

i--

or

i=i-1

and as mentioned in another answer make sure i doesn't go below 0.

I think you ment

i-= 1;

instead of that:

i=-1;

Whoa there that is a little overblown for this problem. Nested loops are they key here…come take a look

public int[] fix34(int[] nums) {
  for(int a = 0; a < nums.length; a++){ //we see 4's first
  for(int b = 0; b < nums.length - 1; b++){ //then the nested loop finds a 3 
  //length - 1 to stay in bounds, although not needed here...
  if(nums[a] == 4 && nums[b] == 3){
  //swap

  int tmp = nums[b + 1];
  nums[b + 1] = nums[a];
  nums[a] = tmp;
  }
  }
  }
  return nums;
}