题解 | 躲藏

//算法学习第四题，DP
#include <bits/stdc++.h>
using namespace std;

//using ll=long long;
const long long MOD = 2000120420010122;
//int 最大只有 $2 \times 10^9$，会爆，必须用 long long

void solve(){
    string s;
    while(cin >> s)
    {
        long long num_c{0};
        long long num_cw{0};
        long long num_cwb{0};
        long long ans{0};
        //ll dp0=0,dp1=0,dp2=0,ans=0;

        for(char ch : s)
        {
            if(ch >= 'A' && ch <= 'Z') ch += 32;//转换大小写

            if(ch == 'c')//可能是开头或结尾
            {
                ans = (ans + num_cwb) % MOD;
                num_c = (num_c + 1) % MOD;
            }
            else if(ch == 'w')
            {
                num_cw = (num_cw + num_c) % MOD;
            }
             else if(ch == 'b')
            {
                num_cwb = (num_cwb + num_cw) % MOD;
            }
        }
        cout << ans << "\n";
    }
}


int main() {
   ios::sync_with_stdio(false);
   cin.tie(0);

   solve();
   return 0;
   
}
// 64 位输出请用 printf("%lld")