POJ 2559 Largest Rectangle in a Histogram ——笛卡尔树

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>

#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <vector>
#include <iostream>
#include <queue>
using namespace std;

#define maxn 100005
#define ll long long

int read()
{
	int x=0,f=1; char ch=getchar();
	while (ch<‘0‘||ch>‘9‘) {if (ch==‘-‘) f=-1; ch=getchar();}
	while (ch>=‘0‘&&ch<=‘9‘) {x=x*10+ch-‘0‘; ch=getchar();}
	return x*f;
}

struct node{
	int id,h;
}a[maxn];
int sta[maxn],top=0,ch[maxn][2],fa[maxn],siz[maxn],n,rt;

void dfs(int k)
{
	if (!k) return ;
	dfs(ch[k][0]);
	dfs(ch[k][1]);
	siz[k]=siz[ch[k][0]]+siz[ch[k][1]]+1;
}

int main()
{
	while (scanf("%d",&n)!=EOF&&n)
	{
		for (int i=1;i<=n;++i) ch[i][0]=ch[i][1]=fa[i]=0;
		for (int i=1;i<=n;++i) a[i].h=read(),a[i].id=i;
		ch[1][0]=ch[1][1]=fa[1]=0; top=0;
		sta[++top]=1;
		siz[1]=1;
		rt=1;
		for (int i=2;i<=n;++i)
		{
			int flag=0,now;
			while (top&&a[sta[top]].h>a[i].h) now=sta[top--],flag=1;
			if (!flag)
			{
				ch[a[sta[top]].id][1]=i;
				fa[i]=a[sta[top]].id;
				sta[++top]=i;
			}
			else
			{
				if (top)
				{
					int z=ch[a[sta[top]].id][1];
					ch[a[sta[top]].id][1]=i;
					fa[i]=a[sta[top]].id;
					ch[i][0]=z;
					fa[z]=i;
					sta[++top]=i;
				}
				else
				{
					fa[now]=i;
					rt=i;
					ch[i][0]=now;
					sta[++top]=i;
				}
			}
		}
		dfs(rt);
		ll ans=0;
		for (int i=1;i<=n;++i) ans=max(ans,(ll)siz[i]*(ll)a[i].h);
		printf("%lld\n",ans);
	}
}