【CCF-CSP】201812-2-小明放学100分（含详细注释）

#include <iostream>
using namespace std;
int main()
{   //灯顺序为 红、绿、黄 循环
    int red,yellow,green;//红、黄、绿灯的额定时间
    int n;//经过道路/红绿灯总数
    long long SumTime=0;//小学上学所用时间
    cin>>red>>yellow>>green;
    cin>>n;
    for(int i=0;i<n;i++){
        int k,t;
        cin>>k>>t;
        if(k==0){
            SumTime=SumTime+t;
        }
        else if(k==1){//初始为红灯
            int time=SumTime%(red+yellow+green);
            if(time<=t){SumTime=SumTime+t-time;}//此轮回没有走出红灯
            else if(t+green<=time && time<t+green+yellow){SumTime=SumTime+(t+green+yellow-time)+red;}//到达时已变为绿灯变为黄灯
            else if(t+green+yellow<=time && time<t+green+yellow+red){SumTime=SumTime+(t+green+yellow+red-time);}//此轮回出红灯后再次进入红灯
        }
        else if(k==2){//初始为黄灯
            int time=SumTime%(red+yellow+green);
            if(time<t){//没有走出黄灯
                SumTime=SumTime+t-time+red;
            }
            else if(t<=time &&time<t+red ){//到达时为红灯
                SumTime=SumTime+(t+red-time);
            }
            else if(t+red+green<=time && time<t+red+green+yellow){SumTime=SumTime+(t+green+yellow+red-time)+red;}//此轮回中出了黄灯再次进入黄灯
        }
        else if(k==3){//初始为绿灯
            int time=SumTime%(red+yellow+green);
            if(t<time &&time<t+yellow){//到达时为黄灯
                SumTime=SumTime+(t+yellow-time)+red;
            }
            else if(t+yellow<time && time<t+yellow+red){//到达时为红灯
                SumTime=SumTime+(t+yellow+red-time);
            }
            //此轮回第1、2次进入绿灯对SumTime没有影响
        }
    }
    cout<<SumTime<<endl;
    return 0;
}