POJ 1201 Intervals （差分约束）

//9063355	NKHelloWorld	1201	Accepted	30788K	469MS	C++	1825B	2011-08-02 19:12:01
#include <cstdio>
using namespace std;
int n,maxb = 0,dis[51000];
struct EDGE
{
int from,to,d;
};
EDGE edge[51000][50];
int pedge[51000];

int spfa(int s)
{
int i,a,b,d;
bool inque[51000];
int que[51000],tail = 0,head = 0;
for(i=0;i<=maxb;i++)
{
inque[i] = false;
dis[i] = -2147483647;
}
dis[s] = 0;
inque[s] = true;
que[tail++] = s;
while(head<tail)
{
a = que[head%maxb];
inque[a] = false;
head++;
for(i=0;i<pedge[a];i++)
{
b = edge[a][i].to;
d = edge[a][i].d;
if(dis[b] < dis[a]+d)
{
dis[b] = dis[a]+d;
if(inque[b]==false)
que[tail++%maxb] = b;
}
}
}
return 0;
}

int main()
{
int i,j,a,b,d;
EDGE now;
scanf("%d",&n);
for(i=1;i<=n;i++)
{
scanf("%d%d%d",&a,&b,&d);
now.from = a;   now.to = b+1;   now.d = d;
if(now.to > maxb)
maxb = now.to;
edge[a][pedge[a]++] = now;
}
for(i=1;i<=maxb;i++)
{
now.from = i;   now.to = i-1;   now.d = -1;
edge[now.from][pedge[now.from]++] = now;
now.from = i-1; now.to = i;     now.d = 0;
edge[now.from][pedge[now.from]++] = now;
}
for(i=0;i<=maxb;i++)
{
now.from = maxb+1;  now.to = i; now.d = 0;
edge[now.from][pedge[now.from]++] = now;
}
spfa(maxb+1);
printf("%d\n",dis[maxb]-dis[0]);
return 0;
}