poj3231

简单模拟，题意描述不清晰，我来仔细描述一下，flashget在下载一些文件，每个文件有一个初始大小，初始速度，最大速度。当一个文件下载结束后，他的速度（占用的带宽）会平均分配给别的任务（各文件的速度增加值相同），假设我们要把速度x分配给a个文件，那么就要给每个文件分配x/a的速度，前提条件是分配后该文件的速度不超过其最大速度。若超过了则不能给他分配这么多，只让它达到其最大速度即可。这样一来我们的下载速度就会有剩余，因为受到最大速度的限制，有些文件并没有被分配到x/a这么多的速度。对于剩余的速度怎么处理呢？就是除去那几个已经到达最大速度的文件，其余文件按照刚才的方法再分配一次剩余速度。模拟即可。这题精度很难控制，我开始试着用先将所有到达最大速度的进程先处理，最后再计算平均值的方法，居然是错的，理论上这种做法比上述做法精度高。

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#include <iostream>

#include <cstdlib>

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;



#define maxn 105



struct Elem

{

    double size, speed, max_speed;

} elem[maxn];



int n, m;

double time_left[maxn];

bool finished[maxn];

double ans[maxn];

double reached[maxn];

int task_left;



void input()

{

    scanf("%d", &m);

    for (int i = 0; i < n; i++)

        scanf("%lf%lf%lf", &elem[i].size, &elem[i].speed, &elem[i].max_speed);

}



void cal_time()

{

    for (int i = 0; i < n; i++)

        if (!finished[i])

            time_left[i] = elem[i].size / elem[i].speed;

}



void size_reduce(double min_time)

{

    for (int i = 0; i < n; i++)

        if (!finished[i])

            elem[i].size -= min_time * elem[i].speed;

}



int get_min()

{

    int ret = 0;

    while (finished[ret])

        ret++;

    for (int i = ret + 1; i < n; i++)

        if (!finished[i] && time_left[i] < time_left[ret])

            ret = i;

    return ret;

}



void distribute(double bandwidth)

{

    double band_left = bandwidth;

    int num = 0;

    for (int i = 0; i < n; i++)

        if (!finished[i] && !reached[i])

            num++;

    if (num == 0)

        return;

    double average;

    while (band_left > 0)

    {

        average = band_left / num;

        bool did = false;

        for (int i = 0; i < n; i++)

        {

            if (finished[i] || reached[i])

                continue;

            did = true;

            if (elem[i].max_speed - elem[i].speed < average)

            {

                band_left -= elem[i].max_speed - elem[i].speed;

                elem[i].speed = elem[i].max_speed;

                reached[i] = true;

                num--;

            }else

            {

                band_left -= average;

                elem[i].speed += average;

            }

        }

        if (!did)

            break;

    }

}



void work()

{

    memset(finished, 0, sizeof(finished));

    memset(reached, 0, sizeof(reached));

    double now_time = 0;

    task_left = n;

    while (task_left > 0)

    {

        cal_time();

        int next_task = get_min();

        finished[next_task] = true;

        task_left--;

        double bandwidth = elem[next_task].speed;

        double min_time = time_left[next_task];

        size_reduce(min_time);

        now_time += min_time;

        ans[next_task] = now_time;

        distribute(bandwidth);

    }

}



int main()

{

    //freopen("t.txt", "r", stdin);

    int t = 0;

    while (scanf("%d", &n), n)

    {

        t++;

        printf("Case %d:\n", t);

        input();

        work();

        for (int i = 0; i < n; i++)

            printf("NO%d:%.3fs\n", i + 1, ans[i]);

    }

    return 0;

}