HDU/HDOJ 1025 Constructing Roads In JGShining's Kingdom（道路问题，LIS）

http://acm.hdu.edu.cn/showproblem.php?pid=1025

Constructing Roads In JGShining's Kingdom

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 23250    Accepted Submission(s): 6648

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.
   
  

题意：

贫穷的城镇需要富裕的城镇帮助，实现帮助需要在两者之间修路。

问题的要求是，任何两个路不能够有交叉。

思路：

参考题解后，在之前就不知道怎么用 LIS 

如图：当 1和 6 有道路的时候，其余2 - 5 之间的道路都是违法的，可以用LIS思想求解。

Code：

#include<stdio.h>
#include<string.h>
const int MYDD=1103+5e5;

int MAX(int x,int y) {
	return x>y? x:y;
}

int flag,n;
int link[MYDD];//需要连接的序号
int dd[MYDD];
int Dichotomy(int x,int y) { //二分查找
	int left=1,right=y;
	while(left<=right) {
		int middle=(left+right)/2;
		if(x>dd[middle])	left=middle+1;
		else				right=middle-1;
	}
	flag=MAX(flag,left);
	return left;
}

void LIS(int a[]) {
	flag=1;
	dd[1]=a[0];
	for(int j=1; j<n; j++)
		dd[Dichotomy(a[j],flag)]=a[j];
}

int main() {
	int TT=1;
	while(scanf("%d",&n)!=EOF) {
		memset(dd,0,sizeof(dd));
		for(int j=0; j<n; j++) {
			int poor,rich;
			scanf("%d%d",&poor,&rich);
			link[poor-1]=rich-1;
		}

		LIS(link);
		printf("Case %d:\n",TT++);//注意 road 单复数的问题
		if(flag==1)	 printf("My king, at most %d road can be built.\n",flag);
		else		 printf("My king, at most %d roads can be built.\n",flag);
		puts("");
	}
	return 0;
}