POJ 1716 Integer Intervals 差分约束

题目：http://poj.org/problem?id=1716

#include <stdio.h>
#include <string.h>
#include <vector>
#include <queue>

const int INF = 0x3f3f3f3f;

struct Edge
{
    int v, w;
    Edge(){};
    Edge(int v, int w)
    {
        this->v = v;
        this->w = w;
    }
};

std::vector<Edge>map[10010];
int dist[10010];
bool inque[10010];

void spfa(int s)
{
    std::queue<int>q;
    memset(inque, 0, sizeof(inque));
    dist[s] = 0;
    q.push(s);
    inque[s] = 1;
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        inque[u] = 0;
        for(int i = 0; i < map[u].size(); i++)
        {
            int v = map[u][i].v;
            if(dist[v] < dist[u] + map[u][i].w)
            {
                dist[v] = dist[u] + map[u][i].w;
                if(!inque[v])
                {
                    q.push(v);
                    inque[v] = 1;
                }
            }
        }
    }
}

int main()
{
    int n;
    int x, y;
    while(scanf("%d", &n) != EOF)
    {
        for(int i = 0; i <= 10001; i++)
        {
            map[i].clear();
        }
        int low = INF, high = 0;
        for(int i = 0; i < n; i++)
        {
            scanf("%d %d", &x, &y);
            map[x].push_back(Edge(y+1, 2));
            if(low > x)low = x;
            if(high < y)high = y;
        }
        for(int i = low; i <= high+1; i++)
        {
            map[0].push_back(Edge(i, 0));
            map[i].push_back(Edge(i+1, 0));
            map[i+1].push_back(Edge(i, -1));
            dist[i] = -INF;
        }
        map[0].push_back(Edge(high+1, 0));
        spfa(low);
        printf("%d\n", dist[high+1] - dist[low]);
    }
    return 0;
}