%300为0的个数（牛客第四场）-- number

题意：

给你一串数，问你如题。

思路：

我不是这样的作法，从后往前，先取00，再算%3==0的个数，往前推的时候有递推关系：

#define IOS ios_base::sync_with_stdio(0); cin.tie(0);
#include <cstdio>//sprintf islower isupper
#include <cstdlib>//malloc  exit strcat itoa system("cls")
#include <iostream>//pair
#include <fstream>
#include <bitset>
//#include <map>
//#include<unordered_map>
#include <vector>
#include <stack>
#include <set>
#include <string.h>//strstr substr
#include <string>
#include <time.h>//srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;
#include <cmath>
#include <deque>
#include <queue>//priority_queue<long long, vector<long long>, greater<long long> > q;//less
#include <vector>//emplace_back
//#include <math.h>
//#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor
#include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)
using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation
#define fo(a,b,c) for(register long long a=b;a<=c;++a)
#define fr(a,b,c) for(register long long a=b;a>=c;--a)
#define mem(a,b) memset(a,b,sizeof(a))
#define pr printf
#define sc scanf
void swapp(long long &a,long long &b);
double fabss(double a);
long long maxx(long long a,long long b);
long long minn(long long a,long long b);
long long Del_bit_1(long long n);
long long lowbit(long long n);
long long abss(long long a);
//const long long INF=(1LL<<60);
const double E=2.718281828;
const double PI=acos(-1.0);
const long long inf=(1<<29);
const double ESP=1e-9;
const long long mod=(long long)1e9+7;
const long long N=(long long)1e6+6;
 
char s[N];
long long ans=0;
 
int main()
{
    sc("%s",s+1);
    s[0]='&';
    long long l=strlen(s)-1;
    long long cont=0;
    long long cnt[4]={0,0,0,0},temp=0;
    fr(i,l,1)
    {
        temp+=s[i]-'0';
        temp%=3;
        cnt[temp]++;
        if(s[i]=='0')
            cont++;
    }
    fr(i,l,1)
    {
        if(s[i]==s[i+1]&&s[i]=='0')
        ans+=cnt[0];
        temp=s[i]-'0';
        temp%=3;
        if(temp==0)
            cnt[0]--;
        else if(temp==1)
        {
            long long a=cnt[2],b=cnt[1],c=cnt[0];
            cnt[0]=b-1;cnt[1]=a,cnt[2]=c;
        }
        else
        {
            long long a=cnt[2],b=cnt[1],c=cnt[0];
            cnt[0]=a-1,cnt[1]=c,cnt[2]=b;
        }
    }
 
    pr("%lld
",ans+cont);
    return 0;
}
 
/**************************************************************************************/
 
long long maxx(long long a,long long b)
{
    return a>b?a:b;
}
 
void swapp(long long &a,long long &b)
{
    a^=b^=a^=b;
}
 
long long lowbit(long long n)
{
    return n&(-n);
}
 
long long Del_bit_1(long long n)
{
    return n&(n-1);
}
 
long long abss(long long a)
{
    return a>0?a:-a;
}
 
double fabss(double a)
{
    return a>0?a:-a;
}
 
long long minn(long long a,long long b)
{
    return a<b?a:b;
}