2017-2018 ACM-ICPC, NEERC, Southern Subregional Contest, qualification stage (Online Mirror, ACM-ICPC Rules, Teams Preferred) E. Packmen

题意：p得走到*，同时出发，可转弯，只需要有p走过就行，问最短时间

思路：二分时间，然后判断该p在该时间能走完多少个*，再看所有p走完是否*都被走过

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+100;

vector<int  > p,star;
string ch;
int n;

bool hh(int q,int ll,int  rr ,int time){
    int xx=min(abs(q-ll)+abs(ll-rr),abs(q-rr)+abs(ll-rr));
    if(xx>time) return false;
    return true;
}

bool check(int time){
    int ll=0;
    for(int i=0;i<p.size();i++){
        int rr=ll;
        while(rr<star.size()&&hh(p[i],star[ll],star[rr],time))
            rr++;
        ll=rr;
    }
    if(ll==star.size()) return true;
    return false;
}
int main(){
    int n;
    scanf("%d",&n);
    cin>>ch;
    for(int i=0;i<ch.size();i++){
        if(ch[i]=='P') p.push_back(i);
        else if(ch[i]=='*') star.push_back(i);
    }
    int l=0,r=1e9,mid,ans;
    while(l<=r){
        mid=(l+r)>>1;
        if(check(mid)){
            ans=mid;
            r=mid-1;
        }
        else l=mid+1;
    }
    cout<<ans<<endl;
}