POJ 1201 Intervals （差分约束）

POJ1716的变形，数据规模增大，用了循环数组。

//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;
}