クイックソート

QuickSort.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class QuickSort {

    private static final int LEFT = 0;
    private static final int RIGHT = 1;
    
    protected static void exchange(int[] a, int i, int j) {
        int temp = a[i];
        a[i] = a[j];
        a[j] = temp;
    }
    
    protected static int rearrange(int[] a, int i, int j) {
        int mover = LEFT;
        while (i < j) {
            if (mover == LEFT) {
                if (a[i] > a[j]) {
                    exchange(a, i, j);
                    mover = RIGHT;
                } else {
                    i++;
                }
            } else {
                if (a[i] > a[j]) {
                    exchange(a, i, j);
                    mover = LEFT;
                } else {
                    j--;
                }
            }
        }
        return i;
    }
    
    public static void sort(int[] a, int i, int j) {
        if (i < j) {
            int p = rearrange(a, i, j);
            sort(a, i, p-1);
            sort(a, p+1, j);
        }
    }
    
    public static void main(String[] args) throws IOException {
        int a[] = new int[10];
        InputStreamReader in = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(in);
        System.out.println("10個の整数を入力してください");
        for (int i = 0; i < 10; i++) {
            a[i] = Integer.valueOf(br.readLine());
        }
        sort(a, 0, 9);
        System.out.println("\nソート結果");
        for (int i : a) {
            System.out.println(i);
        }
    }

}