极大化思想——洛谷 P1578 奶牛浴场

#include<bits/stdc++.h>
#define Ll long long
using namespace std;
const int N=5e3+5;
struct cs{int x,y;}d
;
int n,m,t,ans;
bool cmp1(cs a,cs b){return a.y<b.y;}
bool cmp2(cs a,cs b){return a.x<b.x;}
bool cmp3(cs a,cs b){return a.y>b.y;}
void work(){
for(int i=1;i<=t;i++){
int ma=n,mi=0;
for(int j=i+1;j<=t;j++){
if(d[j].x>ma||d[j].x<mi)continue;
ans=max(ans,abs(d[i].y-d[j].y)*(ma-mi));
if(d[j].x<d[i].x)mi=d[j].x;else ma=d[j].x;
if(ma==mi)break;
}
}
}
int main()
{
scanf("%d%d%d",&n,&m,&t);
for(int i=1;i<=t;i++)scanf("%d%d",&d[i].x,&d[i].y);
d[++t].x=0;d[t].y=0;d[++t].x=n;d[t].y=m;
d[++t].x=0;d[t].y=m;d[++t].x=n;d[t].y=0;
sort(d+1,d+t+1,cmp2);
for(int i=2;i<=t;i++)ans=max(ans,m*(d[i].x-d[i-1].x));
sort(d+1,d+t+1,cmp1);work();
sort(d+1,d+t+1,cmp3);work();
printf("%d",ans);
}