字符串中子序列出现次数【模板题】

形如：题意：给一个字符串，求子序列“xyz...x”出现的次数

两道板子题：https://ac.nowcoder.com/acm/contest/3947/I

 https://ac.nowcoder.com/acm/contest/87/B【注意：是否区分大小写】

 1 #include<bits/stdc++.h>
 2 
 3 using namespace std;
 4 #define int long long
 5 #define mod 20010905 
 6 int dp[66];
 7 signed main(){
 8     string s;
 9     cin>>s;
10     
11     for(int i=0;i<s.size();i++){
12         s[i]=tolower(s[i]);
13         dp[8]=(dp[8]+(s[i]=='u')*dp[7])%mod;
14         dp[7]=(dp[7]+(s[i]=='o')*dp[6])%mod;
15         dp[6]=(dp[6]+(s[i]=='y')*dp[5])%mod;
16         dp[5]=(dp[5]+(s[i]=='e')*dp[4])%mod;
17         dp[4]=(dp[4]+(s[i]=='v')*dp[3])%mod;
18         dp[3]=(dp[3]+(s[i]=='o')*dp[2])%mod;
19         dp[2]=(dp[2]+(s[i]=='l')*dp[1])%mod;
20         dp[1]=(dp[1]+(s[i]=='i'))%mod;
21     }
22     cout<<dp[8];
23     return 0;
24 }

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int inf=1<<30;
 4 typedef long long ll;
 5 const double pi=acos(-1);
 6 const int mod=2000120420010122;
 7 const int maxn=2e5+7;
 8 ll dp[5];
 9 int main(){
10     string s;
11     while(cin>>s){
12     memset(dp,0,sizeof(dp));
13     for(int i=0;i<s.length();i++){
14         s[i]=tolower(s[i]);            
15             dp[4]=(dp[4]+(s[i]=='c')*dp[3])%mod;
16             dp[3]=(dp[3]+(s[i]=='b')*dp[2])%mod;
17             dp[2]=(dp[2]+(s[i]=='w')*dp[1])%mod;
18             dp[1]=(dp[1]+(s[i]=='c'))%mod;            
19     }
20     cout<<dp[4]<<endl;
21     }
22     return 0;
23 }