HDOJ1015(简单深搜)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int SIZE=13;
char a[5];
int vis[SIZE*2+10];
bool cmp(char a,char b)
{
    return b > a;
}

int npow(int x,int n)
{
    int res=1;
    while(n)
    {
        if(n&1)    res*=x;
        x*=x;
        n>>=1;
    }
    
    return res;
}

bool check(long long target)
{
    long long ans=0;
    for(int i=0;i<5;i++)
    {
        if((i+1)%2==1)
            ans+=npow(a[i]-‘A‘+1,i+1);
        else
            ans-=npow(a[i]-‘A‘+1,i+1);
    }
    if(ans==target)
        return true;
    
    return false;
}

char out[6];
void dfs(int i,char op[],long long target)
{
    if(i==5)
    {
        if(check(target))
        {
            for(int j=0;j<5;j++)
                out[j]=a[j];
        }
        
        return ;
    }
    for(int j=0;op[j];j++)
    {
        int it=op[j]-‘A‘+1;
        if(!vis[it])
        {
            vis[it]=1;
            a[i]=op[j];
            dfs(i+1,op,target);
            vis[it]=0;
            a[i]=‘\0‘;            
        }            
    }
}
int main()
{
    
    long long target;
    char op[SIZE]={‘\0‘};
    while(scanf("%lld %s",&target,&op)!=EOF&&target!=0&&strcmp(op,"END")!=0)
    {
        sort(op,op+strlen(op),cmp);
        memset(out,‘\0‘,sizeof(out));
        memset(a,‘\0‘,sizeof(a));
        dfs(0,op,target);
        if(out[0]==‘\0‘)
            printf("no solution\n");
        else
            printf("%s\n",out);
        memset(op,‘\0‘,sizeof(op));
    }
    
    return 0;
}