The even number of an integer queue is placed in the front, the odd number is placed in the back, and the relative position of the even and odd numbers remains unchanged

Ideas ：
Go through the array ,
1. use 2 Pointers from the array header , Tail scan ;
Head pointer check even , Tail pointer check odd ;
2. Use an empty array , To store the scanned even numbers , Odd number ; Even numbers start at the head of the array , Odd numbers start at the end of the array ;

    public  static void sort(int[] a){
    
        int[] b = new int[a.length];
        int m =0;
        int n = b.length-1;
        for (int i = 0; i <a.length ; i++) {
    
            if(a[i] % 2 ==0){
    // even numbers 
                b[m]=a[i];
                m++;
            }
            if(a[a.length-1-i] %2 !=0){
    // Odd number 
                b[n]=a[a.length-1-i];
                n--;
            }
        }
       
    }