poj_1716Integer Intervals

Integer Intervals

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 11782		Accepted: 4964

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

#include<iostream>
#include<cstdio>
#include<cstring>
#include<map>
#include<cmath>
#include<vector>
#include<algorithm>
#include<set>
#include<string>
#include<queue>
#include <stack>
using namespace std;
#pragma warning(disable : 4996)
const int MAXN = 10005;
const int INF = 999999;

typedef struct Node 
{
	int v;//终点位置
	int value;//权值
	int next;//同一起点下在edge数组中的位置
}Node;
Node edge[MAXN * 4];//邻接表
int first[MAXN];//以该点为起点的第一条边在edge数组中的位置
int n; //n点数
bool visited[MAXN];
int dist[MAXN];
queue<int>Q;
int MIN, MAX;

void init()
{
	int x, y, index;
	memset(first, -1, sizeof(first));
	index = 1;
	MIN = INF;
	MAX = -INF;
	for (int i = 1; i <= n; i++)
	{
		scanf("%d %d", &x, &y);
		y++;
		if(x < MIN)
		{
			MIN = x;
		}
		if(y > MAX)
		{
			MAX = y;
		}
		edge[index].v = y;
		edge[index].value = 2;
		edge[index].next = first[x];
		first[x] = index++;
	}
	//cout << MIN << " " << MAX << endl;
	for (int i = MIN; i < MAX; i++)
	{
		edge[index].v = i + 1;
		edge[index].value = 0;
		edge[index].next = first[i];
		first[i] = index++;

		edge[index].v = i;
		edge[index].value = -1;
		edge[index].next = first[i + 1];
		first[i + 1] = index++;
	}

}


void SPFA(int Start)
{
	while (!Q.empty())
	{
		Q.pop();
	}
	for (int i = 0; i <= MAX; i++)
	{
		visited[i] = false;
		dist[i] = -INF;
	}
	dist[Start] = 0;
	visited[Start] = true;
	Q.push(Start);
	while (!Q.empty())
	{
		int top = Q.front();
		Q.pop();
		visited[top] = false;
		for (int i = first[top]; i != -1 ; i = edge[i].next)
		{
			int e = edge[i].v;
			if(dist[e] < edge[i].value + dist[top])
			{
				dist[e] = edge[i].value + dist[top];
				if(!visited[e])
				{
					Q.push(e);
					visited[e] = true;
				}
			}
		}
	}
}

int main()
{
	freopen("in.txt", "r", stdin);
	while (scanf("%d", &n) != EOF)
	{
		init();
		SPFA(MIN);
		printf("%d\n", dist[MAX]);
		//print();
	}
	return 0;
}