Codeforces 801C Voltage Keepsake 结构体sort排序+贪心

Posted 2020-09-11

#include <bits/stdc++.h>
using namespace std;
struct In{
    long long a, b;
    double t;
}s[100005];
bool cmp(In p, In q) {
    if(p.t < q.t)
        return true;
    else if(p.t == q.t && p.a < q.a)
        return true;
    return false;

}
int main() {
    long long n, p;

    scanf("%lld%lld", &n, &p);
    long long sum1 = 0;
    for(long long i = 0; i < n; i++) {
        scanf("%lld%lld", &s[i].a, &s[i].b);
        sum1 += s[i].a;
        s[i].t = s[i].b * 1.0 / s[i].a;
    }

    if(sum1 <= p) {
        printf("-1\n");
    }
    else {
        sort(s, s + n, cmp);
        //for(int i = 0; i < n; i++)
        //    printf("%lld--a %lld--b %.9f--t\n\n", s[i].a, s[i].b, s[i].t);
        double time = s[0].t;
        double pow = s[0].t * p;
        double dis, x;
        long long sum = s[0].a;
        long long i = 1;
        while(i < n) {
            dis = s[i].t - time;
            if(sum > p) {
                x = pow / (sum - p);
                if(x <= dis) {
                    printf("%.10f\n", time + x);
                    break;
                }

            }
            pow = pow + dis * (p - sum);
            sum += s[i].a;
            time = s[i].t;
            i++;
        }
        if(i == n) {
            x = pow / (sum - p);
            printf("%.10f\n", time + x);
        }
    }


    return 0;
}