P1015 回文数

#include<cstdio>
#include<cctype>
#include<vector>
#include<cstring>
#include<algorithm>
#define maxn 2333
using namespace std;
char buf[maxn];
int n;
vector<int> a,b;
int main()
{
	scanf("%d%s",&n,buf);
	for(int i=0,len=strlen(buf);i<len;i++)
	{
		if(buf[i]>='0'&&buf[i]<='9') a.push_back(buf[i]-'0');
		else a.push_back(islower(buf[i])?buf[i]-'a'+10:buf[i]-'A'+10);  
	}
	b=a;
	reverse(a.begin(),a.end());
	if(a==b) 
	{
		puts("STEP=0");
		return 0;
	}
	for(int ans=1;ans<=30;ans++)
	{
		for(int i=0,siz=a.size();i<siz;i++)
		{
			a[i]+=b[i];
			if(i!=siz-1) a[i+1]+=a[i]/n;
			else if(a[i]>=n) a.push_back(a[i]/n);
			a[i]%=n; 
		}
		b=a;
		reverse(b.begin(),b.end());
		if(a==b) 
		{
			printf("STEP=%d",ans);
			return 0;
		}
	}
	puts("Impossible!");
	return 0;
}