UVa 10474 Where is the Marble?

题目：http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=108&page=show_problem&problem=1415
快排+二分，就是不知道跟回溯法有什么关系。

#include<stdio.h>
#include<stdlib.h>
#define MAXN 10000+10

int marble[MAXN];

int cmp(void const *a,void const *b)
{
	return *((int *)a)-*((int *)b);
}
int binsearch(int find,int *marble,int left,int right)
{
	int mid=(left+right)/2;
	while(left<right)
	{
		if(marble[mid]<find)
			left=mid+1;
		else
			right=mid;
		mid=(left+right)/2;
	}
	if(marble[mid]==find) return mid+1;
	else return 0;
}
int main()
{
	int i,N,Q,cases=0;;
	for(;;)
	{
		scanf("%d%d",&N,&Q);
		if(N==0&&Q==0) break;		
		cases++;
		printf("CASE# %d:\n",cases);
		for(i=0;i<N;i++)
			scanf("%d",marble+i);
		qsort(marble,N,4,cmp);
		while(Q--)
		{
			int find,res;
			scanf("%d",&find);
			res=binsearch(find,marble,0,N-1);
			if(res)
				printf("%d found at %d\n",find,res);
			else
				printf("%d not found\n",find);
		}
	}
	return 0;
}