A

https://vjudge.net/contest/218366#problem/A

中间溢出，注意求模。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<cmath>
#include<vector>
#include<stack>
#include<queue>
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define IO ios::sync_with_stdio(false);cin.tie(0);
#define INF 0x3f3f3f3f
#define MAXN 100010
const int MOD=1e9+7;
typedef __int64 ll;
using namespace std;
char s[MAXN];
ll a[MAXN],maxm;
int main()
{
    IO;
    while(cin >> s){
        maxm = -INF ;
        ll len = strlen(s);
        for(int i = 0; i < len; i++){
            if(s[i] >= '0'&&s[i] <= '9'){
                a[i] = s[i]-'0';
                maxm = max(maxm, a[i]);
            }
            else{
                a[i] = s[i]-'A'+10;
                maxm = max(maxm, a[i]);
            }
        }
        ll flag=0, loc, r, sum;
        ll beg = max((ll)2, maxm)+1;//起点必须加一 
        for(int i = beg; i <= 36; i++){
            r=1;sum=0;
            for(int j = 0; j < len; j++){//中间溢出，求模的技巧 
                sum = (sum+a[len-1-j]*r%(i-1))%(i-1);
                r = r*i%(i-1);
            }        
            if(sum==0){
                flag=1;loc=i;
                break;
            }
        }
        if(!flag) cout << "No Solution" << endl;
        else cout << loc << endl;
    }
    return 0;
}