1628: [Usaco2007 Demo]City skyline

1628: [Usaco2007 Demo]City skyline

Time Limit: 5 Sec   Memory Limit: 64 MB
Submit: 348   Solved: 284
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Description

Input

第一行给出N，W

第二行到第N+1行:每行给出二个整数x,y，输入的x严格递增，并且第一个x总是1

Output

输出一个整数，表示城市中最少包含的建筑物数量

Sample Input

10 26
1 1
2 2
5 1
6 3
8 1
11 0
15 2
17 3
20 2
22 1

INPUT DETAILS:

The case mentioned above

Sample Output

6

HINT

Source

 

单调栈。。。一个月前居然傻逼的写不出来。。

#include<stack>
#include<cstdio>
#include<iostream>
using namespace std;

const int maxn = 5e4 + 50;

long long ans = 0;
int x[maxn],y[maxn],n,i,j,w;
stack <int> s;

int main()
{
	#ifdef YZY
		freopen("yzy.txt","r",stdin);
	#endif
	cin >> n >> w;
	for (i = 1; i <= n; i++) scanf("%d%d",&x[i],&y[i]);
	y[i] = 0;
	for (i = 1; i <= n + 1; i++)
	{
		if (s.empty())
		{
			s.push(i);
			continue;
		}
		int tail = 1E9;
		while (!s.empty() && y[s.top()] > y[i])
		{
			int T = y[s.top()];
			s.pop();
			if (T != tail) tail = T,++ans;
		}
		s.push(i);
	}
	cout << ans;
	return 0;
}