Safecracker-HDU1015

题意

给你大写字母的字符串，A=1,...Z=26，以及target
问你是否有v - w^2 + x^3 - y^4 + z^5 = target
有输出字典序大的那个字符串

分析

dfs

code

#include<iostream>
#include<string.h>
#include<algorithm>
#include<string>
#include<math.h>
using namespace std;
#define ll long long
char s[20],a[20];
int n,vis[20],len;
bool cmp(const char &a,const char &b){
    return a>b;
}
int dfs(int sum,int step){
    if(step==5){
        if(sum==n) return 1;
        else return 0;
    }
    int tem;
    if(step&1) tem=-1;
    else tem=1;
    for(int i=0;i<len;i++)
    {
        if(!vis[i]){
            vis[i]=1;
            int x=s[i]-'A'+1;
            int nsum=sum+tem*pow(x,step+1);
            if(dfs(nsum,step+1)){
                a[step]=s[i];
                return 1;
            }
                vis[i]=0;
        }
    }
    return 0;
}
int main(){
    //freopen("in.txt","r",stdin);
    while(cin>>n>>s&&n&&s!="END"){
        len=strlen(s);
        sort(s,s+len,cmp);
        memset(vis,0,sizeof(vis));
        if(dfs(0,0)) cout<<a<<endl;
        else cout<<"no solution\n"; 
    }
    return 0;
}