HDU 1025 Constructing Roads In JGShining's Kingdom

HDU 1025 ;链接：http://acm.hust.edu.cn/vjudge/contest/view.action?cid=42656#overview；

题目：

Constructing Roads In JGShining's Kingdom

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 14226    Accepted Submission(s): 4048

Problem Description

JGShining's kingdom consists of 2n(n is no more than 500,000) small cities which are located in two parallel lines.

Half of these cities are rich in resource (we call them rich cities) while the others are short of resource (we call them poor cities). Each poor city is short of exactly one kind of resource and also each rich city is rich in exactly one kind of resource. You may assume no two poor cities are short of one same kind of resource and no two rich cities are rich in one same kind of resource.

With the development of industry, poor cities wanna import resource from rich ones. The roads existed are so small that they're unable to ensure the heavy trucks, so new roads should be built. The poor cities strongly BS each other, so are the rich ones. Poor cities don't wanna build a road with other poor ones, and rich ones also can't abide sharing an end of road with other rich ones. Because of economic benefit, any rich city will be willing to export resource to any poor one.

Rich citis marked from 1 to n are located in Line I and poor ones marked from 1 to n are located in Line II.

The location of Rich City 1 is on the left of all other cities, Rich City 2 is on the left of all other cities excluding Rich City 1, Rich City 3 is on the right of Rich City 1 and Rich City 2 but on the left of all other cities ... And so as the poor ones.

But as you know, two crossed roads may cause a lot of traffic accident so JGShining has established a law to forbid constructing crossed roads.

For example, the roads in Figure I are forbidden.



In order to build as many roads as possible, the young and handsome king of the kingdom - JGShining needs your help, please help him. ^_^

 

Input

Each test case will begin with a line containing an integer n(1 ≤ n ≤ 500,000). Then n lines follow. Each line contains two integers p and r which represents that Poor City p needs to import resources from Rich City r. Process to the end of file.

 

Output

For each test case, output the result in the form of sample.
You should tell JGShining what's the maximal number of road(s) can be built.

 

Sample Input

  

   2
1 2
2 1
3
1 2
2 3
3 1
  

 

Sample Output

  

   Case 1:
My king, at most 1 road can be built.

Case 2:
My king, at most 2 roads can be built.


   

    Hint
   
   

    
Huge input, scanf is recommended.

   
   


   
   

    解题思路： 
   
   

    这道题实质上是一道最长递增子序列问题，我们要求的事一组数据p，对应一组数据r，之间连接的桥的最大的数目，我们可以用p作为数组下标，r作为数组元素，这样的话，数组的最长递增子序列即为所求解（如果在最长递增子序列中添加元素，必然会导致出现相交的情况）。这里我是用map来标记p和r的，这样就不需要对p进行排序了。
   
   


   
   

    代码：
   
   

    
#include <iostream>
#include <map>
#include <cstring>
using namespace std;

const int MAXN = 500010;
int n, dp[MAXN], b[MAXN];
map<int, int> mm;

int binary(int l, int r, int x)
{
	l = 0; r = n;
	while(l < r)
	{
		int mid = (l + r) >> 1;
		if(b[mid + 1] >= x)
			r = mid;
		else
			l = mid + 1;
	}
	return l;
}

int main()
{
	std::ios::sync_with_stdio(false);
	
	int t = 0;
	while(cin >> n)
	{
		memset(dp, 0, sizeof(dp));
		memset(b, 0, sizeof(b));
		mm.clear();
		
		for(int i = 1; i <= n; i++)
		{
			int p, r;
			cin >> p >> r;
			mm[p] = r;
			b[i] = 0x7fffffff;
		}
		b[0] = -100;
		
		for(int i = 1; i <= n; i++)
		{
			dp[i] = binary(1, n, mm[i]) + 1;
			if(mm[i] < b[dp[i]])
			{
				b[dp[i]] = mm[i];
			}
		}
		
		int ans = -1;
		for(int i = 1; i <= n; i++)
		{
			if(dp[i] > ans)
				ans = dp[i];
		}
		
		t++;
		cout << "Case " << t << ":" << endl;
		if(ans > 1)
			cout << "My king, at most " << ans << " roads can be built." << endl;
		else
			cout << "My king, at most " << ans << " road can be built." << endl;
		cout << endl;
	}
	
	return 0;
}