(贪心) poj 1716

Integer Intervals

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 12886		Accepted: 5449

Description

An integer interval [a,b], a < b, is a set of all consecutive integers beginning with a and ending with b. 
Write a program that: finds the minimal number of elements in a set containing at least two different integers from each interval.

Input

The first line of the input contains the number of intervals n, 1 <= n <= 10000. Each of the following n lines contains two integers a, b separated by a single space, 0 <= a < b <= 10000. They are the beginning and the end of an interval.

Output

Output the minimal number of elements in a set containing at least two different integers from each interval.

Sample Input

4
3 6
2 4
0 2
4 7

Sample Output

4

Source

CEOI 1997

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<cstdlib>
#include<algorithm>
#include<queue>
#include<vector>
#include<set>
using namespace std;
int n;
struct node
{
      int x,y;
}e[10010];
bool cmp(node a,node b)
{
      return a.y<b.y;
}
int main()
{
      while(scanf("%d",&n)!=EOF)
      {
            int sum=0;
            for(int i=0;i<n;i++)
                  scanf("%d%d",&e[i].x,&e[i].y);
            sort(e,e+n,cmp);
            int st=e[0].y-1,se=e[0].y;
            for(int i=1;i<n;i++)
            {
                  if(e[i].x<=st)
                        continue;
                  else if(e[i].x<=se)
                  {
                        sum++;
                        st=se;
                        se=e[i].y;
                  }
                  else
                  {
                        sum+=2;
                        st=e[i].y-1;
                        se=e[i].y;
                  }
            }
            printf("%d\n",sum+2);
      }
      return 0;
}