快速排序

public static void quickSort(int[] a, int l, int r){
		
		if(l<r){
			int m = partition(a, l, r);
			quickSort(a, l, m-1);
			quickSort(a, m+1, r);
		}
	}
	/**
	 * easy, from linux
	 */
	private static int partition(int[] a, int l, int r) {
		
		int insert = l;
		int x = a[l];
		for(int i=l+1;i<=r;++i)
			if(a[i]<x)
			{
				a[insert++] = a[i];//将当前insert位置插入a[i],并将insert更新
				a[i] = a[insert];//腾出insert的空间留给下个元素使用
			}
		
		a[insert] = x;
		return insert;
	}