Cod sursa(job #2744271)

Utilizator FunnyStockyMihnea Andreescu FunnyStocky Data 24 aprilie 2021 11:14:12
Problema Flux maxim Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.15 kb
#include <cstdio>
#include <iostream>
#include <queue>
#include <vector>

using namespace std;

struct flow {
  const int INF = (int) 1e9;
  struct edge {
    int cap;
    int to;
    int nxt;
  };
  int n;
  vector<int> pos;
  vector<int> level;
  vector<int> head;
  vector<edge> edges;
  void init(int nn) {
    n = nn;

    pos.clear();
    level.clear();
    edges.clear();
    head.clear();

    head.resize(n + 1, -1);
    pos.resize(n + 1);
    level.resize(n + 1);
  }
  void add(int a, int b, int c) {
    edges.push_back({c, b, head[a]});
    edges.push_back({0, a, head[b]});

    head[a] = (int) edges.size() - 2;
    head[b] = (int) edges.size() - 1;
  }
  int dfs(int a, int cap) {
    if (!cap || a == n) {
      return cap;
    }
    while (pos[a] != -1) {
      int i = pos[a];
      pos[a] = edges[i].nxt;
      if (edges[i].cap > 0 && level[edges[i].to] == 1 + level[a]) {
        int x = dfs(edges[i].to, min(cap, edges[i].cap));
        if (x > 0) {
          edges[i].cap -= x;
          edges[i ^ 1].cap += x;
          return x;
        }
      }
    }
    return 0;
  }
  int get() {
    int sol = 0;
    while (1) {
      for (int i = 1; i <= n; i++) {
        level[i] = -1;
        pos[i] = head[i];
      }
      level[1] = 0;
      queue<int> q;
      q.push(1);
      while (!q.empty()) {
        int a = q.front();
        q.pop();
        int ind = head[a];
        while (ind != -1) {
          int b = edges[ind].to;
          if (edges[ind].cap > 0 && level[b] == -1) {
            level[b] = 1 + level[a];
            q.push(b);
          }
          ind = edges[ind].nxt;
        }
      }
      if (level[n] == -1) {
        break;
      }
      while (1) {
        int x = dfs(1, INF);
        if (x == 0) {
          break;
        }
        sol += x;
      }
    }
    return sol;
  }
};

int main() {
  freopen ("maxflow.in", "r", stdin);
  freopen ("maxflow.out", "w", stdout);
  int n, m;
  cin >> n >> m;
  flow f;
  f.init(n);
  while (m--) {
    int a, b, c;
    cin >> a >> b >> c;
    f.add(a, b, c);
  }
  cout << f.get() << "\n";
  return 0;
}