箭术 (Archery,Seoul 2008,LA 4253)

#include <iostream>
#include <string.h>
#include <string>
#include <fstream>
#include <algorithm>
#include <stdio.h>
#include <vector>
#include <queue>
using namespace std;
const double eps = 1e-8;
#define MAXN 5005
struct Target{
    long double y,l,r;
    Target(long double _y = 0.0, long double _l = 0.0, long double _r = 0.0) {
         y = _y, l = _l, r = _r;
         if (l > r) swap(l, r);
     }
};
vector<Target> rec;
bool cmp(Target a, Target b) {
     return a.y < b.y;
 }

 int test(long double x) {
     long double L = (rec[0].l - x - eps) / rec[0].y, R = (rec[0].r - x + eps) / rec[0].y;
     for(int i=1;i<=(rec.size()- 1);i++) {
         long double tmpL = (rec[i].l - x - eps) / rec[i].y, tmpR = (rec[i].r - x + eps) / rec[i].y;
         if (R < tmpL) return 1;
         if (tmpR < L) return -1;
         L = max(tmpL, L), R = min(tmpR, R);
     }
     return 0;
 }

bool bs(long double w)
{
    long double l=0, r = w, m;
    while (r - l > eps) {
         m = (l + r) / 2.0;
         int res = test(m);
         if (res == 0) {
 //            cout << m << endl;
             return true;
         } else if (res == -1) l = m;
         else r = m;
     }
     return false;
}
int main()
{
    int W,T,n;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&W);
        scanf("%d",&n);
        long double D,L,R;
        rec.clear();
        for(int i=0;i<n;i++)
        {
            cin>>D>>L>>R;
            rec.push_back(Target(D,L,R));
        }
        sort(rec.begin(),rec.end(),cmp);
        bs(W) ? puts("YES") : puts("NO");
    }


    return 0;
}

http://www.cnblogs.com/LyonLys/archive/2013/03/04/LA_4253_Lyon.html

抄袭了下~~ 二分+枚举

有空重写=。=