for (int& i = cur[u]; i; i = e[i].next) {
    int v = e[i].v;
    if (e[i].cap && level[v] == level[u] + 1) {
      long long res = dfs(v, std::min(in, e[i].cap));
      e[i].cap -= res, e[i ^ 1].cap += res;
      in -= res, out += res;
      if (in == 0) break;
    }
  }

复杂度是对的，但是

  for (int& i = cur[u]; i && in; i = e[i].next) {
    int v = e[i].v;
    if (e[i].cap && level[v] == level[u] + 1) {
      long long res = dfs(v, std::min(in, e[i].cap));
      e[i].cap -= res, e[i ^ 1].cap += res;
      in -= res, out += res;
    }
  }

却会TLE

（这是为什么