UVa 1616 Caravan Robbers （二分+贪心）

#include <iostream>
#include <cmath>
#include <cstdlib>
#include <set>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
const int INF = 0x3f3f3f3f;
const double eps = 1e-9;//注意精度
const int maxn = 1e5 + 5;
struct node{
    int l, r;
    bool operator < (const node &p) const{
        return r < p.r;
    }
};
node a[maxn];
int n;

int main(){
//    freopen("in.txt", "r", stdin);
    while(scanf("%d", &n) == 1){
        for(int i = 0; i < n; ++i)
            scanf("%d %d", &a[i].l, &a[i].r);

        double r = 1000000, l = 0, ans = 0;

        sort(a, a+n);
        while(r - l > eps){//二分
            double m = ((l+r)/2.0);
            bool ok = true;
            double s = 0;
            for(int i = 0; i < n; ++i){//贪心
                if(s < a[i].l)  s = a[i].l;
                if(s + m > a[i].r){ ok = false;   break;  }
                s += m;
            }
            if(ok){ ans = m;   l = m;  }
            else   r = m;
        }

        int rp = 0, rq = 1;//小数化分数
        for(int p, q = 1; q <= n; ++q){
            p = round(ans * q);
            if(fabs((double)p/q - ans) < fabs((double)rp/rq - ans)){
                rp = p;  rq = q;  
            }
        }

        printf("%d/%d\n", rp, rq);
    }
    return 0;
}