정렬 알고리즘

정렬 알고리즘

이 글은 C언어로 구현한 정렬 알고리즘을 그대로 Java 로 구현하였습니다.

각각의 알고리즘의 설명과 특징은 위 링크에 들어가셔서 봐주시기 바랍니다.

 

1. 선택정렬(selectionSort)

    void selectSort(int[] arr){

        for(int i = 0; i < arr.length - 1; i++){
            int min = i;
            for(int j = i + 1; j < arr.length; j++){
                if(arr[min] > arr[j]) min = j;
            }
            swap(arr, i, min);
        }
    }

 

2. 버블정렬(bubbleSort)

 

void bubbleSort(int[] arr){
    for(int i = arr.length - 1; i > 0; i--){
        boolean pass = true;
        for(int j = 0; j < i; j++){
            if(arr[j] > arr[j + 1]){
                pass = false;

                swap(arr, j, j + 1);
            }
        }
        if(pass) return;
    }
}

 

3. 삽입정렬(insertitonSort)

void insertSort(int[] arr){
    for (int i = 1; i < arr.length; i++) {
        int temp = arr[i];
        int j = i - 1;
        while(j >= 0 && arr[j] > temp){
            arr[j + 1] = arr[j];
            j--;
        }
        arr[j + 1] = temp;
    }
}

 

4. 퀵정렬(quickSort)

void quickSort(int[] arr){
    quickSort(arr, 0, arr.length - 1);
}

private void quickSort(int[] arr, int start, int end){
    if(start < end){
        int pi = partition(arr, start, end);
        quickSort(arr, start, pi - 1);
        quickSort(arr, pi, end);
    }
}

private int partition(int[] arr, int start, int end){
    int pivot = arr[(start + end) / 2];
    int i = start;
    int j = end;
    while(i < j){
        while(arr[i] < pivot) i++;
        while(arr[j] > pivot) j--;

        swap(arr, i, j);
        i++;
        j--;
    }
    return i;
}

 

5. 병합정렬(mergeSort)

void mergeSort(int[] arr){
    mergeSort(arr, 0, arr.length - 1);
}
private void mergeSort(int[] arr, int start, int end){
    if(start < end){
        int mid = (start + end) / 2;
        mergeSort(arr, start, mid);
        mergeSort(arr, mid + 1, end);

        mergeSort(arr, mid, start, end);
    }
}
private void mergeSort(int[] arr, int mid, int start, int end){
    int arrSize = end - start + 1;
    int a = start;
    int b = mid + 1;
    int k = 0;

    int[] temp = new int[arrSize];

    while(a <= mid && b <= end){
        if (arr[a] <= arr[b]) temp[k++] = arr[a++];
        else temp[k++] = arr[b++];
    }

    while(a <= mid) temp[k++] = arr[a++];
    while(b <= end) temp[k++] = arr[b++];

    for(k = 0, a = start; a <= end; k++, a++){
        arr[a] = temp[k];
    }
}

 

 

위 코드를 하나의 클래스로 묶어서 테스트하기 편하게 만든 코드입니다.

public class Main {
    static final int MAX_SIZE = 100;

    public static void main(String[] args) {

        Random random = new Random();
        int[] arr = new int[MAX_SIZE];

        for(int i = 0; i < MAX_SIZE; i++){
            arr[i] = random.nextInt(MAX_SIZE);
        }

        //for (int num : arr) System.out.print(num + ", ");
        //System.out.println();
        //====================================

        Sort sort = new Sort();

        sort.selectSort(arr);
//        sort.bubbleSort(arr);
//        sort.insertSort(arr);
//        sort.quickSort(arr);
//        sort.mergeSort(arr);

        for (int num : arr) System.out.print(num + ", ");

    }

}

class Sort{
    private void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }

    void selectSort(int[] arr){

        for(int i = 0; i < arr.length - 1; i++){
            int min = i;
            for(int j = i + 1; j < arr.length; j++){
                if(arr[min] > arr[j]) min = j;
            }
            swap(arr, i, min);
        }
    }

    void bubbleSort(int[] arr){
        for(int i = arr.length - 1; i > 0; i--){
            boolean pass = true;
            for(int j = 0; j < i; j++){
                if(arr[j] > arr[j + 1]){
                    pass = false;

                    swap(arr, j, j + 1);
                }
            }
            if(pass) return;
        }
    }

    void insertSort(int[] arr){
        for (int i = 1; i < arr.length; i++) {
            int temp = arr[i];
            int j = i - 1;
            while(j >= 0 && arr[j] > temp){
                arr[j + 1] = arr[j];
                j--;
            }
            arr[j + 1] = temp;
        }
    }

    void quickSort(int[] arr){
        quickSort(arr, 0, arr.length - 1);
    }

    private void quickSort(int[] arr, int start, int end){
        if(start < end){
            int pi = partition(arr, start, end);
            quickSort(arr, start, pi - 1);
            quickSort(arr, pi, end);
        }
    }

    private int partition(int[] arr, int start, int end){
        int pivot = arr[(start + end) / 2];
        int i = start;
        int j = end;
        while(i < j){
            while(arr[i] < pivot) i++;
            while(arr[j] > pivot) j--;

            swap(arr, i, j);
            i++;
            j--;
        }
        return i;
    }

    void mergeSort(int[] arr){
        mergeSort(arr, 0, arr.length - 1);
    }
    private void mergeSort(int[] arr, int start, int end){
        if(start < end){
            int mid = (start + end) / 2;
            mergeSort(arr, start, mid);
            mergeSort(arr, mid + 1, end);

            mergeSort(arr, mid, start, end);
        }
    }
    private void mergeSort(int[] arr, int mid, int start, int end){
        int arrSize = end - start + 1;
        int a = start;
        int b = mid + 1;
        int k = 0;

        int[] temp = new int[arrSize];

        while(a <= mid && b <= end){
            if (arr[a] <= arr[b]) temp[k++] = arr[a++];
            else temp[k++] = arr[b++];
        }

        while(a <= mid) temp[k++] = arr[a++];
        while(b <= end) temp[k++] = arr[b++];

        for(k = 0, a = start; a <= end; k++, a++){
            arr[a] = temp[k];
        }
    }
}