Codevs 1173 最优贸易

#include<queue>
#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;

const int maxx = 500003;
queue<int>q;
int n,m,price[maxx],head[maxx][3],minn[maxx],maxn[maxx],u,v,z;
int num_edge,vis[maxx],ans;
struct Edge{
    int pre,to;
}edge[maxx];

void build_edge(int u,int v) {
    edge[++num_edge].pre = head[u][1];
    edge[num_edge].to = v;
    head[u][1] = num_edge;
    edge[++num_edge].pre = head[v][2];
    edge[num_edge].to = u;
    head[v][2] = num_edge;
}

void init() {
    scanf("%d%d",&n,&m);
    for(int i=1; i<=n; i++) {
        scanf("%d",&price[i]);
        minn[i] = 105; 
    }
    for(int i=1; i<=m; i++) {
        scanf("%d%d%d",&u,&v,&z);
        build_edge(u,v);
        if(z == 2) build_edge(v,u);
    }
}

void min_spfa() {
    q.push(1);
    vis[1] = 1;
    minn[1] = price[1];
    while(!q.empty()) {
        int x=q.front();
        q.pop();
        vis[x] = 0;
        for(int i=head[x][1];i;i=edge[i].pre) {
            int to = edge[i].to;
            if(minn[to] > minn[x] ||minn[to] > price[to]) {
                minn[to] = min(minn[x],price[to]);
                if(!vis[to]) {
                    q.push(to);
                    vis[to] = 1;
                }
            }
        }
    }
}

void max_spfa() {
    q.push(n);
    vis[n] = 1;
    maxn[n] = price[n];
    ans = max(ans,maxn[n]-minn[n]);
    while(!q.empty()) {
        int x=q.front();
        q.pop();
        vis[x] = 0;
        for(int i=head[x][2]; i; i=edge[i].pre) {
            int to = edge[i].to;
            if(maxn[to] < maxn[x] || maxn[to] < price[to]) {
                maxn[to] = max(maxn[x],price[to]);
                ans=max(ans,maxn[to]-minn[to]);
                if(!vis[to]) {
                    q.push(to);
                    vis[to] = 1;
                }
            }
        }
    }
    
}

int main() {
    init();
    min_spfa();
    memset(vis,0,sizeof(vis));
    max_spfa();
    printf("%d\n",ans);
    return 0;
}