codeforces 1236D

传送门：https://codeforces.com/contest/1236/problem/D

代码实现来至大佬：https://blog.csdn.net/weixin_39132605/article/details/102868652

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int maxn=1e5+5;
 
set<int>s1[maxn],s2[maxn];
int main()
{
    int n,m,k;
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=k;i++){
       int x,y;
       scanf("%d%d",&x,&y);
       s1[x].insert(y);s2[y].insert(x);
    }
    for(int i=1;i<=n;i++){
        s1[i].insert(0);s1[i].insert(m+1);
    }
    for(int i=1;i<=m;i++){
        s2[i].insert(0);s2[i].insert(n+1);
    }
    int nowx=1,nowy=1;
    ll ans=1;
    int nx=1,ny=1;
    int maxx=n,maxy=m,minx=1,miny=1;
    for(int i=0;;i++)
    {
        if(i%4==0){
            nx=nowx;
            int pos=*s1[nowx].lower_bound(nowy);
            ny=min(maxy,pos-1);
            minx=nx+1;
        }
        else if(i%4==1){
            ny=nowy;
            int pos=*s2[nowy].lower_bound(nowx);
            nx=min(maxx,pos-1);
            maxy=ny-1;
        }
        else if(i%4==2){
            nx=nowx;
            auto it=s1[nowx].lower_bound(nowy);
            it--;
            int posy=*it;
            ny=max(miny,posy+1);
            maxx=nowx-1;
        }
        else if(i%4==3){
            ny=nowy;
            auto it=s2[nowy].lower_bound(nowx);
            it--;
            int posx=*it;
            nx=max(minx,posx+1);
            miny=nowy+1;
        }
        ans+=abs(nx-nowx)+abs(ny-nowy);
        if(nowx==nx&&nowy==ny){
            if(nowx==1&&nowy==1&&i%4==0){}
            else{break;}
        }
        nowx=nx;nowy=ny;
    }
    if(ans==(ll)n*m-k){
        cout<<"YES"<<endl;
    }
    else{
        cout<<"NO"<<endl;
    }
    return 0;
}