求单调序列的nlogn算法-HDU-1025

Constructing Roads In JGShining's Kingdom

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 11464    Accepted Submission(s): 3283

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

21 22 131 22 33 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.
 

 

最初写的所 n^2复杂度的，超时了。看了别人的代码，才知道可以优化倒 nlogn

由于此题的数据是1到n连续的，可以转化为求最大单调序列。

这里用s[j] 存储在 最大线路条数为 j 时，所连接的的城市的最小下限。更新s[] 时，保证它还是单调递增的，用二分查找优化。

#include <stdio.h>int s[500001];int a[500001];int main(){ int i,p,r,n,len,t=0;     while( ~scanf("%d",&n) )     {    for(i=0;i<n;i++)      {      scanf("%d%d",&p,&r);      a[p-1]=r;      }           s[0]=a[0];len=1; int start,end,mid;           for(i=1;i<n;i++)             {             //如果当前连接,可直接加入,增加总单调序列长度，并把当前长度的上限置为a[i]               if( a[i]>s[len-1] )  s[len++]=a[i];               else{//不可加入，则更新上限值. 保证s[] 所单调递增的               //利用二分查找               start = 0;               end = len-1;               while(start <= end){                   mid = (start + end) / 2;                   if(s[mid] > a[i]) end = mid-1;                   else start = mid+1;               }               s[start]=a[i];               }               for(int k=0; k<=len; k++)               printf("%d ",s[k]);               puts("\n");             }            printf("Case %d:\n",++t);            if(len==1) printf("My king, at most %d road can be built.\n\n",len);            else  printf("My king, at most %d roads can be built.\n\n",len);       }     return 0;}