为什么直接这么写也能过？

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int n, m, a[N], s[N], r;
bool f[N];
vector<int> e[N], g[N];
void I(int u, int c) {
  for (auto v : g[u]) {
    c > s[v] && (s[v] = c, I(v, max(c, a[v])), 1);
  }
}
void S(int u) {
  f[u] = 1;
  r = max(r, s[u] - a[u]);
  for (auto v : e[u]) {
    !f[v] && (S(v), 1);
  }
}
int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; i++) { cin >> a[i]; }
  for (int i = 1, u, v, o; i <= m; i++) {
    cin >> u >> v >> o;
    e[u].push_back(v), g[v].push_back(u);
    o ^ 1 && (e[u].push_back(v), g[u].push_back(v), 1);
  }
  s[n] = a[n], I(n, a[n]), S(1);
  cout << r;
  return 0;
}