C - Emergency Evacuation

https://vjudge.net/contest/394066#problem/C

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <iomanip>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>
#include <iterator>
#include <utility>
#include <sstream>
#include <limits>
#include <numeric>
#include <functional>
using namespace std;
#define gc getchar()
#define mem(a) memset(a,0,sizeof(a))
#define debug(x) cout<<"debug:"<<#x<<" = "<<x<<endl;

#define ios ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int,int> pii;
typedef char ch;
typedef double db;

const double PI=acos(-1.0);
const double eps=1e-6;
const int inf=0x3f3f3f3f;
const int maxn=1e5+10;
const int maxm=100+10;
const int N=1e6+10;
const int mod=1e9+7;

int I[500005] = {0};
int J[500005] = {0};
int t_cnt[1000000] = {0};
int main()
{
    int r , s , p;
    cin >> r >> s >> p;
    int t = 0;
    int max_t = 0;
    int delay = 0;
    int ans = 0;
    for(int i = 0;i<p;i++)
    {
        cin >> I[i] >> J[i];
    }
    for(int i = 0;i<p;i++)
    {
        if(J[i] <= s)
        {
            t = s-J[i]+1 + r-I[i]+1;
        }
        else
        {
            t = J[i]-s + r-I[i]+1;
        }
        //cout<<t <<endl;
        if(t > max_t)
        {
            max_t = t;
        }
        t_cnt[t] ++;
    }
    for(int i = 1;i <= max_t;i++)
    {
        if(t_cnt[i])
        {
            delay += t_cnt[i]-1;
        }
        else
        {
            if(delay > 0)
                delay -= 1;
        }
    }
    //cout<<endl<<delay<<endl;
    ans = max_t + delay;
    /*
    for(int i = 1;i<=max_t;i++)
    {
        cout<<t_cnt[i]<<endl;
    }
    */
    //cout << max_t <<" " <<delay<<endl;
    cout << ans;
    return 0;
}