[Codility] Lesson2. CyclicRotation - 문제풀이

Description

주어진 배열을 오른쪽으로 K만큼 로테이션 하여 결과를 반환하는 문제입니다.

An array A consisting of N integers is given. Rotation of the array means that each element is shifted right by one index, and the last element of the array is moved to the first place. For example, the rotation of array A = [3, 8, 9, 7, 6] is [6, 3, 8, 9, 7] (elements are shifted right by one index and 6 is moved to the first place).

The goal is to rotate array A K times; that is, each element of A will be shifted to the right K times.

Write a function:

class Solution { public int[] solution(int[] A, int K); }

that, given an array A consisting of N integers and an integer K, returns the array A rotated K times.

For example, given

A = [3, 8, 9, 7, 6] K = 3

the function should return [9, 7, 6, 3, 8]. Three rotations were made:

[3, 8, 9, 7, 6] -> [6, 3, 8, 9, 7] [6, 3, 8, 9, 7] -> [7, 6, 3, 8, 9] [7, 6, 3, 8, 9] -> [9, 7, 6, 3, 8]

For another example, given

A = [0, 0, 0] K = 1

the function should return [0, 0, 0]

Given

A = [1, 2, 3, 4] K = 4

the function should return [1, 2, 3, 4]

Assume that:

N and K are integers within the range [0..100];each element of array A is an integer within the range [−1,000..1,000].

In your solution, focus on correctness. The performance of your solution will not be the focus of the assessment.

Solution 1. reverse

public int[] solution(int[] A, int K) {
    int len = A.length;
    if(len == 0) return A;
    K = K%len;
    reverse(A,0,len-1); //step1 전체 reverse [7,6,5,4,3,2,1]
    reverse(A,0,K-1);   //step2 로테이션 숫자들 reverse [ 5,6,7,4,3,2,1 ]
    reverse(A,K,len-1);      //step3 나머지 숫자들 reverse [ 5,6,7,1,2,3,4 ]

    return A;
}

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

Reference

CyclicRotation coding task - Learn to Code - Codility