Watering Grass UVA - 10382

喷水装置的圆心和半径确定，就能确定左端和右端。开始时pos=0,选取左端小于pos，右端最大的更新pos。

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cstring>
#include <map>
#include <queue>
#include <set>
#include <cassert>
#include <stack>
#include <bitset>
#define mkp make_pair
using namespace std;
const double EPS=1e-8;
typedef long long lon;
const lon SZ=330,INF=0x7FFFFFFF,mod=1000000007;

struct nd{
    double ll,rr;
    nd(double a,double b):ll(a),rr(b){}
    bool operator<(const nd& rbs)const
    {
        return ll<rbs.ll;
    }
};

void init(int n,double wid,vector<nd> &vct)
{
    for(int i=0;i<n;++i)
    {
        double pi,ri;
        cin>>pi>>ri;
        if(ri>0.5*wid)
        {
            double delta=sqrt(ri*ri-0.25*wid*wid);
            vct.push_back(nd(pi-delta,pi+delta));
        }
    }
    sort(vct.begin(),vct.end());
}

int work(double len,vector<nd> &vct)
{
    double pos=0;
    int res=0;
    for(int i=0;;)
    {
        double rm=0;
        for(;i<vct.size()&&(vct[i].ll<pos||fabs(vct[i].ll-pos)<EPS);++i)
        {//注意限制i的条件写在前 
            rm=max(rm,vct[i].rr);
        }
        if(fabs(rm)<EPS)return -1;
        pos=rm;
        ++res;
        if(pos>len||fabs(pos-len)<EPS)break;
        if(i>=vct.size())return -1;
    }
    //cout<<res<<endl;
    return res;
}

int main()
{
    std::ios::sync_with_stdio(0);
    //freopen("d:\\1.txt","r",stdin);
    lon casenum;
    //cin>>casenum;
    //cout<<casenum<<endl;
    //for(lon time=1;time<=casenum;++time)
    int n,len,wid;
    for(int time=1;cin>>n>>len>>wid;++time)
    {
        vector<nd> vct;
        init(n,wid,vct);
        cout<<work(len,vct)<<endl;
    }
    return 0;
}

重复。