Codeforces 898F

898F - Restoring the Expression

思路：字符串hash，base是10，事实证明对2e64取模会T（也许ull很费时），对1e9+7取模。

代码：

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define ull unsigned long long
#define mem(a,b) memset(a,b,sizeof(a))

const int N=1e6+5;
const int base=10;
const int MOD=1e9+7;
ll h[N];
ll p[N];
int num[N];
string s;
void init(string s)
{
    int l=s.size();
    h[0]=0;
    for(int i=0;i<l;i++)
    {
        h[i+1]=(h[i]*base+s[i]-'0')%MOD;
    }
    p[0]=1;
    for(int i=1;i<=l;i++)p[i]=(p[i-1]*base)%MOD;
}
ll get(int l,int r)
{
    if(r-l+1<=0||l-1<0||r<0)return 0;
    return ((h[r]-h[l-1]*p[r-l+1])%MOD+MOD)%MOD;
}
bool is(int l,int r)
{
    if(l<0||r>=s.size()-1||l>=r)return false;
    if((r-l>=2&&s[l+1]=='0')||(s.size()>=r+3&&s[r+1]=='0'))return false;
    mem(num,0);
    string s1=s.substr(0,l+1);
    string s2=s.substr(l+1,r-l);
    string s3=s.substr(r+1,s.size()-r-1);
    //cout<<s1<<' '<<s2<<' '<<s3<<endl;
    if(s2.size()>s3.size()||s1.size()>s3.size())return false;
    if(s1.size()<s2.size())swap(s1,s2);
    int tot=1;
    for(int i=s3.size()-1;i>=0;i--)
    {
        if(tot<=s2.size())
        {
            int t=s1[s1.size()-tot]-'0'+s2[s2.size()-tot]-'0'+num[i];
            if(t>=10)
            {
                if(i==0)return false;
                num[i-1]=t/10;
                num[i]=t=t%10;
            }
            if(t!=s3[i]-'0')return false;
        }
        else if(tot<=s1.size())
        {
            int t=s1[s1.size()-tot]-'0'+num[i];
            if(t>=10)
            {
                if(i==0)return false;
                num[i-1]=t/10;
                num[i]=t=t%10;
            }
            if(t!=s3[i]-'0')return false;
        }
        else
        {
            if(num[i]>=10)
            {
                if(i==0)return false;
                num[i-1]=num[i]/10;
                num[i]=num[i]%10;
            }
            if(num[i]!=s3[i]-'0')return false;
        }
        tot++;
    }
    return true;
}
void solve(string s)
{
    init(s);
    int pos=0,_pos=0;
    int l=s.size();
    for(int i=l-1;i>=0;i--)
    {
        int t=l-i;
        ll sumh=get(i+1,l);
        if((get(1,t)+get(t+1,i))%MOD==sumh){
            pos=t-1;
            _pos=i-1;
            if(is(pos,_pos))break;
            else pos=_pos=0;
        }
        if((get(1,t-1)+get(t,i))%MOD==sumh){
            pos=t-2;
            _pos=i-1;
            if(is(pos,_pos))break;
            else pos=_pos=0;
        }
        if((get(1,i-t)+get(i-t+1,i))%MOD==sumh){
            pos=i-t-1;
            _pos=i-1;
            if(is(pos,_pos))break;
            else pos=_pos=0;
        }
        if((get(1,i-t+1)+get(i-t+2,i))%MOD==sumh){
            pos=i-t;
            _pos=i-1;
            if(is(pos,_pos))break;
            else pos=_pos=0;
        }
    }

    for(int i=0;i<=pos;i++)putchar(s[i]);
    putchar('+');
    for(int i=pos+1;i<=_pos;i++)putchar(s[i]);
    putchar('=');
    for(int i=_pos+1;i<l;i++)putchar(s[i]);
    puts("");
    //cout<<pos<<' '<<_pos<<endl;
    //cout<<get(1,1)<<' '<<get(2,22)<<' '<<get(23,44)<<endl;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>s;
    solve(s);
    return 0;
}