[HDOJ1015]Safecracker（DFS, 组合数学）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1015

这都能过……

 #include <algorithm>
 #include <iostream>
 #include <iomanip>
 #include <cstring>
 #include <climits>
 #include <complex>
 #include <fstream>
 #include <cassert>
 #include <cstdio>
 #include <bitset>
 #include <vector>
 #include <deque>
 #include <queue>
 #include <stack>
 #include <ctime>
 #include <set>
 #include <map>
 #include <cmath>

 using namespace std;

 typedef long long ll;
 const ll maxn = ;
 ll aim;
 ll n;
 char str[maxn];
 char ans[maxn];
 char wtf[maxn];
 bool flag;

 ll quickmul(ll x, ll n) {
     ll ans = ;
     ll t = x;
     while(n) {
         if(n & ) {
             ans = (ans * t);
         }
         t = t * t;
         n >>= ;
     }
     return ans;
 }

 int main() {
     // freopen("in", "r", stdin);
     // freopen("out", "w", stdout);
     while(~scanf("%I64d %s", &aim, str)) {
         if(aim ==  && strcmp("END", str) == ) break;
         memset(wtf, , sizeof(wtf));
         n = strlen(str);
         ll nn =  << n;
         flag = ;
         sort(str, str+n, greater<char>());
         for(ll i = ; i < nn; i++) {
             ll cnt = ;
             memset(ans, , sizeof(ans));
             for(ll j = ; j < n; j++) {
                 if(( << j) & i) {
                     ans[cnt++] = str[j];
                 }
             }
             if(cnt != ) continue;
             sort(ans, ans+cnt);
             do {
                 ll tmp = ans[] - 'A' + ;
                 for(ll k = ; k < cnt; k++) {
                     tmp += quickmul(-, k) * quickmul(ans[k]-'A'+, k+);
                 }
                 if(tmp == aim) {
                     flag = ;
                     if(strcmp(wtf, ans) < ) {
                         strcpy(wtf, ans);
                     }
                 }
             }while(next_permutation(ans, ans+cnt));
         }
         if(!flag) printf("no solution\n");
         else printf("%s\n", wtf);
     }
     return ;
 }