洛谷 1365 WJMZBMR打osu! / Easy

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int N=3e6+5;
int n;
double dp[N],len[N];
char ch[N];
int main()
{
    scanf("%d%s",&n,ch+1);
    for(int i=1;i<=n;i++)
    {
        if(ch[i]==‘x‘){
            len[i]=0;dp[i]=dp[i-1];
        }
        if(ch[i]==‘o‘){
            len[i]=len[i-1]+1;
            dp[i]=dp[i-1]+2*len[i-1]+1;
        }
        if(ch[i]==‘?‘){
            len[i]=(len[i-1]+1)/2;
            dp[i]=dp[i-1]+(2*len[i-1]+1)/2;
        }
    }
    printf("%.4lf",dp[n]);
    return 0;
}