【代码积累】quick sort

import java.awt.image.PixelInterleavedSampleModel;


public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		//int[] test = {5,4,3,2,1};
		int[] test={49,38,65,97,76,13,27,49,78,34,12,64,5,4,62,99,98,54,56,17,18,23,34,15,35,25,53,51};
		quickSort(test,0,test.length-1);
		
		for(int i=0;i<test.length;i++) {
			System.out.format("%d ", test[i]);
		}
		System.out.format("\r");
	}

	
	public static void quickSort(int[] a,int left,int right) {  //left，right是下标
		if( left >= right ) {
			return;
		}
		
		/*选出pivot的index作为参考，根据pivot对原数组进行划分，再分别对左右子数组递归调用quickSort*/
		//此处选择二分法选择pivot
		int pivotIndex = (left+right)/2;
		
		//调用partition，根据pivotValue对数组进行重排
		int regroupIndex = partition(a,left,right,pivotIndex);
		
//		for(int i=0;i<a.length;i++) {
//			System.out.format("%d ", a[i]);
//		}
//		System.out.format("\r");
		
		quickSort(a, left, regroupIndex-1);
		quickSort(a, regroupIndex+1, right);
	}
	
	public static int partition(int[] a,int left,int right,int pivotIndex) {
		int pivotValue = a[pivotIndex];
		int tmp = 0;  //用来swap
		
		//将pivotValue移动到数组尾
		tmp = pivotValue;
		a[pivotIndex] = a[right];
		a[right] = pivotValue;
				
		//逐个遍历 [left,right-1]的元素，将比pivotValue小的元素尽量往前放，同时storeIndex递增，最终storeIndex就是pivotValue该放的位置（storeIndex右边都是比pivotValue大的元素）
		int storeIndex = left;
		for(int i=left;i<=right-1;i++) {  //这里的left，right是实际的下标
			if( a[i] < pivotValue ) {
				//交换a[i]和a[storeIndex],storeIndex递增
				tmp = a[i];
				a[i] = a[storeIndex];
				a[storeIndex] = tmp;
				
				storeIndex++;
			}
		}
		
		//比较结束，比pivotValue小的元素都在 storeIndex的左边，大的元素在右边,交换a[storeIndex]与a[right]
		tmp = a[storeIndex];
		a[storeIndex] = a[right];
		a[right] = tmp;
		
		return storeIndex;
	}
}