Problem p01825 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
using ld = long double;
using point = complex<ld>;

const ld eps = 1e-10;
const ld INF = 1e9;

struct edge {
  int to, cap;
  ld cost;
  int rev;
  edge(int to_, int cap_, ld cost_, int rev_)
      : to(to_), cap(cap_), cost(cost_), rev(rev_) {}
};

const int MAX = 10000;

int V;

vector<edge> G[MAX];
ld h[MAX], dist[MAX];
int prevv[MAX], preve[MAX];

void add(int from, int to, int cap, ld cost) {
  G[from].emplace_back(to, cap, cost, G[to].size());
  G[to].emplace_back(from, 0, -cost, G[from].size() - 1);
}

ld calc(int s, int t, int f) {
  using pii = pair<ld, int>;
  ld res = 0;
  fill(h, h + V, 0);
  while (f > 0) {
    priority_queue<pii, vector<pii>, greater<pii>> que;
    fill(dist, dist + V, INF);
    dist[s] = 0;
    que.emplace(0, s);
    while (!que.empty()) {
      pii p = que.top();
      que.pop();
      int v = p.second;
      if (dist[v] < p.first)
        continue;
      for (size_t i = 0; i < G[v].size(); i++) {
        edge &e = G[v][i];
        if (e.cap > 0 && dist[e.to] > dist[v] + e.cost + h[v] - h[e.to] + eps) {
          dist[e.to] = dist[v] + e.cost + h[v] - h[e.to];
          prevv[e.to] = v;
          preve[e.to] = i;
          que.emplace(dist[e.to], e.to);
        }
      }
    }
    assert(dist[t] < INF / 2);
    for (int v = 0; v < V; v++)
      h[v] += dist[v];
    int d = f;
    for (int v = t; v != s; v = prevv[v]) {
      d = min(d, G[prevv[v]][preve[v]].cap);
    }
    f -= d;
    res += d * h[t];
    for (int v = t; v != s; v = prevv[v]) {
      edge &e = G[prevv[v]][preve[v]];
      e.cap -= d;
      G[v][e.rev].cap += d;
    }
  }
  return res;
}

int main() {
  ios::sync_with_stdio(false), cin.tie(0);
  cout << fixed << setprecision(10);
  int n;
  cin >> n;
  int sx, sy;
  cin >> sx >> sy;
  point s(sx, sy);
  ld res = 0;
  vector<point> f(n), t(n);
  for (int i = 0; i < n; i++) {
    int x, y;
    cin >> x >> y;
    f[i] = point(x, y);
    cin >> x >> y;
    t[i] = point(x, y);
    res += abs(f[i] - t[i]);
  }
  V = n * 2 + 2;
  int src = n * 2, sink = n * 2 + 1;
  for (int i = 0; i < n; i++) {
    add(src, n + i, 1, 0);
    add(i, sink, 1, 0);
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      add(n + i, j, 1, abs(t[i] - f[j]));
    }
  }
  res += calc(src, sink, n);
  cout << res << endl;
  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#define int long long
using namespace std;
using ld = long double;
using point = complex<ld>;

const ld INF = 1e9;

struct edge {
  int to, cap;
  ld cost;
  int rev;
  edge(int to_, int cap_, ld cost_, int rev_)
      : to(to_), cap(cap_), cost(cost_), rev(rev_) {}
};

const int MAX = 10000;

int V;

vector<edge> G[MAX];
ld h[MAX], dist[MAX];
int prevv[MAX], preve[MAX];

void add(int from, int to, int cap, ld cost) {
  G[from].emplace_back(to, cap, cost, G[to].size());
  G[to].emplace_back(from, 0, -cost, G[from].size() - 1);
}

ld calc(int s, int t, int f) {
  using pii = pair<ld, int>;
  ld res = 0;
  fill(h, h + V, 0);
  while (f > 0) {
    priority_queue<pii, vector<pii>, greater<pii>> que;
    fill(dist, dist + V, INF);
    dist[s] = 0;
    que.emplace(0, s);
    while (!que.empty()) {
      pii p = que.top();
      que.pop();
      int v = p.second;
      if (dist[v] < p.first)
        continue;
      for (size_t i = 0; i < G[v].size(); i++) {
        edge &e = G[v][i];
        if (e.cap > 0 && dist[e.to] > dist[v] + e.cost + h[v] - h[e.to]) {
          dist[e.to] = dist[v] + e.cost + h[v] - h[e.to];
          prevv[e.to] = v;
          preve[e.to] = i;
          que.emplace(dist[e.to], e.to);
        }
      }
    }
    assert(dist[t] < INF / 2);
    for (int v = 0; v < V; v++)
      h[v] += dist[v];
    int d = f;
    for (int v = t; v != s; v = prevv[v]) {
      d = min(d, G[prevv[v]][preve[v]].cap);
    }
    f -= d;
    res += d * h[t];
    for (int v = t; v != s; v = prevv[v]) {
      edge &e = G[prevv[v]][preve[v]];
      e.cap -= d;
      G[v][e.rev].cap += d;
    }
  }
  return res;
}

signed main() {
  ios::sync_with_stdio(false), cin.tie(0);
  cout << fixed << setprecision(10);
  int n;
  cin >> n;
  int sx, sy;
  cin >> sx >> sy;
  point s(sx, sy);
  ld res = 0;
  vector<point> f(n), t(n);
  for (int i = 0; i < n; i++) {
    int x, y;
    cin >> x >> y;
    f[i] = point(x, y);
    cin >> x >> y;
    t[i] = point(x, y);
    res += abs(f[i] - t[i]);
  }
  V = n * 2 + 2;
  int src = n * 2, sink = n * 2 + 1;
  for (int i = 0; i < n; i++) {
    add(src, n + i, 1, 0);
    add(i, sink, 1, 0);
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      add(n + i, j, 1, abs(t[i] - f[j]));
    }
  }
  res += calc(src, sink, n);
  cout << res << endl;
  return 0;
}