poj 1201 Intervals 差分约束+spfa

     利用相互关系进行约束，求最长路

    

/*author:jxylang:C/C++university:China,Xidian University**If you need to reprint,please indicate the source***/#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <queue>#define INF 1E9using namespace std;struct edge{    int len,nn;};int ss,ee,dis[50005];queue<int> q;bool in[50005];vector<edge> map[50005];int spfa(){    int i,now,k,next,t;    while(!q.empty())q.pop();    memset(in,0,sizeof(in));    for(i=ss; i<=ee; i++) dis[i]=-INF;    in[ss]=1;    dis[ss]=0;    q.push(ss);    while(!q.empty())    {        now=q.front();        q.pop();        in[now]=0;        k=map[now].size();        for(i=0; i<k; i++)        {            next=map[now][i].nn;            if(dis[next]>=(t=dis[now]+map[now][i].len))continue;            dis[next]=t;            if(in[next])continue;            q.push(next);            in[next]=1;        }    }    return dis[ee];}int main(){    int i,n,a,b,c;    edge temp;    while(~scanf("%d",&n))    {        for(i=0; i<50005; i++)map[i].clear();        ss=INF;        ee=-1;        while(n--)        {            scanf("%d%d%d",&a,&b,&c);            b++;            if(a<ss)ss=a;            if(b>ee)ee=b;            temp.len=c;            temp.nn=b;            map[a].push_back(temp);        }        for(i=ss; i<=ee; i++)        {            temp.len=0;            temp.nn=i+1;            map[i].push_back(temp);            temp.len=-1;            temp.nn=i;            map[i+1].push_back(temp);        }        printf("%d\n",spfa());    }    return 0;}