数组旋转 返回将一维数组向右旋转k个位置的结果。比如，一维数组{1,2,3,4,5}，k=2时，返回结果{4,5,1,2,3}。要求常数级空间复杂度，允许修改原有数组

public class num4 {


int[] rotateK(int[] A,int k){
if(A==null || k>=A.length) return A;
reverse(A,0,A.length-1);
reverse(A, 0, k-1);
reverse(A, k, A.length-1);
return A;
}

void reverse(int[] A,int start,int end){
while(start<end){
int temp = A[start];
A[start] = A[end];
A[end] = temp;
start++;
end--;
}
}

public static void main(String[] args) {
int[] A = {1,2,3,4,5};
int k = 2;
new num4().rotateK(A, k);
for (int i = 0; i < A.length; i++) {
System.out.print(" " + A[i] + " ");
}
}
}