poj 1716 Integer Intervals(差分约束系统)

Integer Intervals
Time Limit: 1000MS   Memory Limit: 10000K
Total Submissions: 13437   Accepted: 5711

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 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define RR freopen("in.txt","r"m,stdin)
#define WW freopen("out.txt","w",stdout)
#define LL long long
#pragma comment(linker, "/STACK:1024000000,1024000000")
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAXN = 100010;
const double eps = 1e-9;
typedef struct node
{
    int v,w,next;
}Edge;
Edge edge[MAXN];
int Dis[MAXN*3], head[MAXN], Left, Right,top;
bool vis[MAXN];

void Add(int u, int v, int w)
{
    edge[top].v = v;
    edge[top].w = w;
    edge[top].next = head[u];
    head[u] = top++;
}

void SPFA()
{
    for(int i=Left; i<=Right; i++)
        Dis[i] = -INF;
    queueQ;
    Dis[Left] = 0;
    Q.push(Left);
    while(!Q.empty())
    {
        int u = Q.front();
        Q.pop();
        vis[u] = false;
        for(int i=head[u]; i!=-1; i=edge[i].next)
        {
            int v = edge[i].v;
            int w = edge[i].w;
            if(Dis[v] < Dis[u] + w)
            {
                Dis[v] = Dis[u] + w;
                if(!vis[v])
                {
                    Q.push(v);
                    vis[v] = true;
                }
            }
        }
    }
}

int main()
{
    int n,u,v;
    while(~scanf("%d",&n))
    {
        top = 0;
        memset(head, -1, sizeof(head));
        memset(vis, false, sizeof(vis));
        memset(edge, 0, sizeof(edge));
        Left = INF, Right = -INF;
        for(int i=0;i




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