Poj 3159 Candies

又是一个简单的差分约束

第一次发现spfa不仅可以用队列，还可以用栈，感觉好神奇

顺便存一下代码

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<stack>
using namespace std;


const int maxn = 31234;
const int maxm = 151234;

struct Edge{
    int next;
    int to;
    int v;
    Edge(){}
    Edge(int next,int to,int v):next(next),to(to),v(v){}
};

Edge edge[maxm];
int head[maxn],top;



void init(int n){
    memset(head,-1,sizeof(head));
    top = 0;
}


void Link(int st,int ed,int v){
    edge[top] = Edge(head[st],ed,v);
    head[st] = top++;
}

bool vis[maxn];
int dis[maxn];
stack<int> Q;

int spfa(int st,int end){
    while(Q.empty()==false){
        Q.pop();
    }
    memset(dis,0x3f,sizeof(dis));
    dis[st] = 0;
    vis[st] = true;
    Q.push(st);
    while(Q.empty()==false){
        st = Q.top();
        vis[st] = false;
        Q.pop();
        for(int i = head[st];~i;i = edge[i].next){
            int ed = edge[i].to;
            int v = edge[i].v;
            if(dis[ed] > dis[st] + v){
                dis[ed] = dis[st] + v;
                if(vis[ed] == false){
                    Q.push(ed);
                    vis[ed] = true;
                }
            }
        }
    }
    return dis[end];
}


int main(){
    int n,m;
    while(~scanf("%d %d",&n,&m)){
        init(n);
        int x,y,v;
        while(m--){
            scanf("%d %d %d",&x,&y,&v);
            Link(x,y,v);
        }
        printf("%d\n",spfa(1,n));
    }
    return 0;
}