Codeforces 628B - New Skateboard

628B - New Skateboard

思路：dp

代码：

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define ls rt<<1,l,m
#define rs rt<<1|1,m+1,r
const int INF=0x3f3f3f3f;
const int N=3e5+5;
ll dp[N]={0};
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    string s;
    cin>>s;
    ll ans=0;
    if((s[0]-‘0‘)%4==0)dp[0]=1;
    for(int i=1;i<s.size();i++)
    {
        int x=s[i]-‘0‘;
        if(x%4==0)dp[i]=dp[i-1]+1;
        else dp[i]=dp[i-1];
        int y=s[i-1]-‘0‘;
        int n=y*10+x;
        if(n%4==0)dp[i]+=i;
    }
    cout<<dp[s.size()-1]<<endl;
    return 0;
}