P1073 最优贸易

https://www.luogu.org/problemnew/show/P1073

#include<bits/stdc++.h>
using namespace std;
#define oo 1<<18;
const int maxn = 100010;
struct u {
    int v,len; 
};
int n, m, v[maxn], d[maxn*3+1];
vector<u> G[maxn*3+1];

void addedge(int x,int y) {
  G[x].push_back((u){y,0});
  G[x+n].push_back((u){y+n,0});//第二层图我从n+1到2n进行编号 
  G[x+2*n].push_back((u){y+2*n,0});//第三层图我从2*n+1到3*n进行编号 
  G[x].push_back((u){y+n,-v[x]});
  G[x+n].push_back((u){y+2*n,v[x]});
  return;
}

queue<int> Q;
bool inq[maxn*3+1];

void spfa() {
  for(int i = 1;i <= n;i++)    d[i] = -oo;
  d[1] = 0;
  inq[1] = true;
  Q.push(1);
  while(!Q.empty()) {
      int tp = Q.front(); Q.pop();
      inq[tp] = false;
      int len = G[tp].size();
      for(int i = 0;i < len;i++) {
          u x = G[tp][i];
          if(d[x.v] < d[tp] + x.len) {
              d[x.v] = d[tp] + x.len;
              if(inq[x.v] == false) {
                  Q.push(x.v);
          inq[x.v] = true;
              }
          } 
      }
  }
}

int main() {
//    freopen("d.txt","r",stdin);  调试用的 
    cin >> n >> m;
    for(int i = 1;i <= n;i++) cin >> v[i];
    for(int i = 1,x,y,z;i <= m;i++) {
        cin >> x >> y >> z;
        addedge(x,y);
        if(z == 2) addedge(y,x);
    }
    G[n].push_back((u){3*n+1,0});
    G[n*3].push_back((u){3*n+1,0});//超级终点是3*n+1编号 
    n = 3*n + 1; //把n改成超级终点的编号，方便spfa操作 

    spfa();
    cout << d[n] << endl;
    return 0;
}