排序算法之快排算法

快排算法

时间复杂度：O()
空间复杂度：O()

public class QuickSort {
    public static void main(String[] args) {
        int[] num = {3,45,78,64,52,11,64,55,99,11,18};
        System.out.println(arrayToString(num,"未排序"));
        quickSort(num,0,num.length-1);
        System.out.println(arrayToString(num,"排序"));
    }
    private static void quickSort(int[] num, int left, int right) {
        //如果left等于right，即数组只有一个元素，直接返回
        if(left>=right) {
            return;
        }
        int p = pivot(num,left,right);
        quickSort(num,left,p-1);
        quickSort(num,p+1,right);
    }
    private static String arrayToString(int[] arr,String flag) {
        String str = "数组为("+flag+")：";
        for(int a : arr) {
            str += a + "\t";
        }
        return str;
    }
    private static void swap(int[] num,int i,int j){
        if(i<j){
            int temp=num[i];
            num[i]=num[j];
            num[j]=temp;
        }
    }
    private static int pivot(int[] num,int left,int right){
        int key=num[left];
        int i=left, j=right;
        while(i<j){
            while(i<j && num[j]>=key){
                j--;
            }
            while(i<j && num[i]<=key){
                i++;
            }
            swap(num,i,j);
        }
        num[left]=num[i];
        num[i]=key;
        return i;
    }
}