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;
}