A - K进制下的大数

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+;
 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 = ; i < len; i++){
             if(s[i] >= ''&&s[i] <= ''){
                 a[i] = s[i]-'';
                 maxm = max(maxm, a[i]);
             }
             else{
                 a[i] = s[i]-'A'+;
                 maxm = max(maxm, a[i]);
             }
         }
         ll flag=, loc, r, sum;
         ll beg = max((ll), maxm)+;//起点必须加一
         for(int i = beg; i <= ; i++){
             r=;sum=;
             for(int j = ; j < len; j++){//中间溢出，求模的技巧
                 sum = (sum+a[len--j]*r%(i-))%(i-);
                 r = r*i%(i-);
             }
             if(sum==){
                 flag=;loc=i;
                 break;
             }
         }
         if(!flag) cout << "No Solution" << endl;
         else cout << loc << endl;
     }
     return ;
 }