swust oj 648--简单字典(数位dp)

 1 /*******************数位dp*************************/
 2 #include <iostream>
 3 #include <cstring>
 4 using namespace std;
 5 
 6 int n, bit[11], judge[27], flag;
 7 char s[11];
 8 
 9 int dfs(int pos, int istrue, bool limit, bool fzero){
10     if (pos < 0) return 1;
11     int last = limit ? bit[pos] : 26;
12     int ret = 0;
13     for (int i = fzero ? 0 : 1; i <= last; i++){
14         //允许多个前导零
15         if (!fzero&&istrue&(1 << i)) continue;
16         ret += dfs(pos - 1, istrue | (1 << i), limit&&i == last, fzero&&!i);
17     }
18     return ret;
19 }
20 
21 int main(){
22     while (cin >> s){
23         n = strlen(s);
24         flag = 0;
25         memset(judge, 0, sizeof(judge));
26         for (int i = n; i >= 1; i--){
27             bit[n - i] = s[i - 1] - ‘a‘ + 1;
28             if (!judge[bit[n - i]]) judge[bit[n - i]] = 1;
29             else {
30                 flag = 1;
31                 break;
32             }
33         }
34         if (flag) cout << "ERROR\n";
35         else cout << dfs(n - 1, 0, 1, 1) - 1 << endl;
36     }
37     return 0;
38 }