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[];
 int dist[];
 bool inque[];

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

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