操作系统（模拟题，HNOI2003）

题意

输入输出

思路

用优先队列维护等待进程，同时用两个变量分别维护当前时间和当前进程。
每当一个新进程到来时，看看再其到来之前，又有哪些进程执行完毕。
然后再与当前优先级最高的进程比较优先级，进行简单的分类讨论。
最后不要忘记，所有进程都进来之后，再将他们从优先队列中弹出，直到优先队列为空为止。

代码

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>

using namespace std;

struct Process
{
    int id, gettime, exetime, importance;
    int starttime;
    
    bool operator < (const Process &p) const
    {
        if(importance != p.importance) return importance < p.importance;
        return gettime > p.gettime;
    }
};

typedef struct Process process;

int main()
{
    int a, b, c, d;
    priority_queue<process> heap;
    int time = 0;
    scanf("%d%d%d%d", &a, &b, &c, &d);
    process p = {a, b, c, d, b};
    process tmp = p;
    heap.push(p);
    while(~scanf("%d%d%d%d", &a, &b, &c, &d)) {
        process p = {a, b, c, d};
        while(heap.size() && tmp.starttime + tmp.exetime <= p.gettime) {
            printf("%d %d\n", tmp.id, tmp.starttime + tmp.exetime);
            int t = tmp.starttime + tmp.exetime;
            heap.pop();
            if(heap.size()) {
                tmp = heap.top();
                tmp.starttime = t;
            }
        }
        if(heap.size()) {
            tmp.exetime -= p.gettime - tmp.starttime;
            tmp.starttime = p.gettime;
        }
        time = p.gettime;
        if(!heap.size()) {
            p.starttime = time;
            heap.push(p);
            tmp = p;
            continue;
        }
        if(p < tmp) {
            heap.push(p);
            tmp.exetime -= time - tmp.starttime;
            tmp.starttime = time;
            heap.pop();
            heap.push(tmp);
        }
        else {
            tmp.exetime -= time - tmp.starttime;
            heap.pop();
            heap.push(tmp);
            p.starttime = time;
            heap.push(p);
            tmp = p;
        }
    }
    while(heap.size()) {
        tmp = heap.top();
        tmp.starttime = time;
        printf("%d %d\n", tmp.id, tmp.starttime + tmp.exetime);
        time = tmp.starttime + tmp.exetime;
        heap.pop();
    }
    return 0;
}