zoj 3196

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=3321

回溯，dfs实现，注意要用long long， 9个100相乘最大数需要long long表示。

#include <iostream>
#include <cstdio>
using namespace std;
long long a[20];
int n;
int k;
long long ans;
const long long inf = 1000000000000000LL;
long long myabs(long long  nn){
  return nn < 0 ? -nn : nn;
}
bool isOk(long long num){
   if(num == 0 && k == 0)
   	  return false;
   num = myabs(num);
   while(num){
     if(num % 10 == k)
     	return false;
  	 num /= 10;
   }
   return true;
}
void dfs(long long res, int index){
   if(index == n){
     if(isOk(res)){
       if(ans < res){
         ans = res;
	   }
	 }
	 return ;
   }  
   
   dfs(res + a[index], index + 1);
   dfs(myabs(res - a[index]), index + 1);
   dfs(res * a[index], index + 1);
   if(a[index]){
     dfs(res / a[index], index + 1);
   }
}
int main()
{
	int t;
	scanf("%d", &t);
	while(t--){
		ans = -inf;
		scanf("%d%d", &n, &k);
		for(int i = 0; i < n; i++){
		  scanf("%d", &a[i]);
		}
		dfs(a[0], 1);
		if(ans != -inf)
		  printf("%lld\n", ans);
        else 
           printf("No result\n");
	}
}