poj 3159

差分约束

我也忘了谁说的了，反正我记得有人说过，只要是差分约束问题都可以转换成图

至少目前看来都是这样的

我一开始spfa+queue超时

看别人博客才知道要用spfa+stack，感觉智商又下降了一点

#include <iostream>
#include <cstdio>
#include <queue>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;
const int maxn = 30005;
int head[maxn];
int nex[150005];
int cnt;
int dis[maxn];
bool vis[maxn];
struct node
{
    int v;
    int w;
};
node mp[150005];
int n,m;
void adde(int a,int b,int c)
{
    mp[cnt].v = b;
    mp[cnt].w = c;
    nex[cnt] = head[a];
    head[a] = cnt++;
}
long long spfa()
{
    memset(dis,0x3f,sizeof(dis));
    memset(vis,0,sizeof(vis));
    int stac[maxn];
    int top = 0;
    stac[top++] = 1;
    dis[1] = 0;
    vis[1] =true;
    while(top)
    {
        int u = stac[--top];
        vis[u] = false;
        for(int i = head[u]; i != -1; i = nex[i])
        {
            //cout << u << " " << mp[i].v  << " " << mp[i].w << endl;
            if(dis[mp[i].v] > dis[u] + mp[i].w)
            {
                dis[mp[i].v] = dis[u] + mp[i].w;
                //cout<< mp[i].v << " " << dis[mp[i].v] << endl;
                if(vis[mp[i].v] == false)
                {
                    stac[top++] = mp[i].v;
                    vis[mp[i].v] = true;
                }
            }
        }
    }
    return dis[n];
}
int main()
{
    //while(scanf("%d%d",&n,&m) != EOF)
    //{
    memset(mp,0,sizeof(mp));
    scanf("%d%d",&n,&m);
    cnt = 0;
    memset(head,-1,sizeof(head));
    for(int i = 0; i < m; ++i)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        adde(a,b,c);
    }
    printf("%d\n",spfa());
    //}
}