Codeforces Round #578 (Div. 2)E. Compress Words（字符串hash）

https://codeforc.es/contest/1200/problem/E

hash匹配后缀和前缀，不断更新hash值

#define bug(x) cout<<#x<<" is "<<x<<endl
#define IO std::ios::sync_with_stdio(0)
#include <bits/stdc++.h>
#define iter ::iterator
#define pa pair<int,int>
using namespace  std;
#define ll long long
#define mk make_pair
#define pb push_back
#define se second
#define fi first
#define ls o<<1
#define rs o<<1|1
const int N=1e6+5;
int n;
ll mod[5]={1000000009,998244353};
ll base[5]={666127,777131};
ll p[N][2];
ll h[N][2];
void init(){
    for(int i=0;i<2;i++)p[0][i]=1;
    for(int i=1;i<=N-2;i++){
        for(int j=0;j<2;j++){
            p[i][j]=p[i-1][j]*base[j]%mod[j];
        }
    }
}
ll cal(int l,int r,int t){
    return (h[r][t]-h[l-1][t]*p[(r-l+1)][t]%mod[t]+mod[t])%mod[t];
}
ll get(char c){
    if('a'<=c&&c<='z')return c-'a';
    if('A'<=c&&c<='Z')return c-'A'+26;
    if('0'<=c&&c<='9')return c-'0'+52;
}
string s,t;
int main(){
    IO;
    cin>>n;
    cin>>s;
    int pre=1;
    init();
    for(int g=1;g<n;g++){
        cin>>t;
        int ns=s.length();
        for(int i=pre;i<=ns;i++){
            ll c=get(s[i-1]);
            for(int j=0;j<2;j++){
                h[i][j]=(h[i-1][j]*base[j]%mod[j]+c)%mod[j];
            }
        }
        int nt=t.length();
        ll H[2]={0};
        pre=ns+1;
        int id=0;
        for(int i=1;i<=nt;i++){
            int f=0;
            ll c=get(t[i-1]);
            for(int j=0;j<2;j++){
                H[j]=(H[j]*base[j]%mod[j]+c)%mod[j];
                if(cal(ns-i+1,ns,j)==H[j])f++;
            }
            if(f==2){
                id=i;
            }
            if(i==ns)break;
        }
        s+=t.substr(id,nt-id);
    }
    cout<<s<<endl;
}
/*
7
RAtONC14epz KfIenADgDKDci OMmOOQOc yVrfGLV49fW1 xntodZLM5 2f7LXdzX xIhm
5
I want to order pizza
*/