HDOJ -- 1015

1.DFS

 #include<cmath>
 #include<cstdio>
 #include<cstdlib>
 #include<string>
 #include<cstring>
 #include<iostream>
 #include<algorithm>
 using namespace std;
 char str[], ans[];
 int vis[], flag;
 bool cmp(char a, char b){return a > b;}
 void dfs(int dep, int target, int len){
     if(dep == ){
         int sum = ;
         for(int i = ; i <= ; i ++)
             sum += (int)pow(ans[i-]-'A'+., i)*(int)pow(-., i+);
         if(sum == target){
             flag = ;
             printf("%s\n", ans);
         }
         return ;
     }
     for(int i = ;  i < len; i ++){
         if(!vis[i]){
             vis[i] = ;
             ans[dep] = str[i];
             dfs(dep+, target, len);
             if(flag) return;
             vis[i] = ;
         }
     }
 }
 int main(){
     int target;
     freopen("in.c", "r", stdin);
     while(~scanf("%d%s", &target, str) && strcmp(str, "END") && target){
         flag = ;
         memset(vis, , sizeof(vis));
         int len = strlen(str);
         sort(str, str+len, cmp);
         dfs(, target, len);
         if(!flag) printf("no solution\n");
         memset(str, , sizeof(str));
     }
     return ;
 }

2,二进制枚举

 #include<iostream>
 #include<cstdio>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 using namespace std;
 int main(){
     int n, a[];
     string str;
     freopen("in.c", "r", stdin);
     while(cin >> n >> str && str != "END" && n){
         char ans[] = "A";
         int flag = ;
         for(int i = ;i < ( << str.size()); i ++){
             int cnt = , sum = ;
             for(int j = ; j < str.size(); j ++){
                 if(i & ( << j)) a[cnt++] = j;
             }
             if(cnt == ){
                 char tmp[];
                 for(int i = ; i < ; i ++) tmp[i] = str[a[i]];
                 sort(tmp, tmp+);
                 do{
                     int sum = ;
                     for(int i = ; i <= ; i ++)
                         sum += (int)pow(-., i+)*(int)pow(tmp[i-]-'A'+., i);
                     if(sum == n){
                         flag = ;
                         if(strcmp(ans, tmp) < ) strcpy(ans, tmp);
                     }
                 }while(next_permutation(tmp, tmp+cnt));
             }
         }
         if(flag) printf("%s\n", ans);
         else cout << "no solution" << endl;
     }
     return ;
 }