Cod sursa(job #2741156)

Utilizator FunnyStockyMihnea Andreescu FunnyStocky Data 15 aprilie 2021 16:59:14
Problema Flux maxim Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.21 kb
#include <iostream>
#include <cstdio>
#include <vector>
#include <queue>

using namespace std;

struct flow {
  struct edge {
    int to;
    int cap;
    int spre;
  };
  const int INF = (int) 1e9;
  int n;
  vector<int> head;
  vector<edge> edges;
  vector<int> level;
  vector<int> pt;

  void init(int nn) {
    n = nn;
    edges.clear();
    head.resize(n + 1, -1);
    pt.resize(n + 1);
    level.resize(n + 1);
  }

  void add(int a, int b, int c, int d = 0) {
    edges.push_back({b, c, head[a]});
    edges.push_back({a, d, head[b]});

    head[a] = (int) edges.size() - 2;
    head[b] = (int) edges.size() - 1;
  }

  int dfs(int a, int cap) {
    if (cap == 0 || a == n) {
      return cap;
    }
    while (pt[a] != -1) {
      int i = pt[a];
      if (edges[i].cap && level[edges[i].to] == 1 + level[a]) {
        int b = edges[i].to;
        int x = dfs(b, min(cap, edges[i].cap));
        if (x > 0) {
          edges[i].cap -= x;
          edges[i ^ 1].cap += x;
          return x;
        }
      }
      pt[a] = edges[pt[a]].spre;
    }
    return 0;
  }

  int get() {
    int ret = 0;
    while (1) {
      for (int i = 1; i <= n; i++) {
        level[i] = -1;
        pt[i] = 0;
      }
      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) {
          if (edges[ind].cap > 0) {
            int b = edges[ind].to;
            if (level[b] == -1) {
              level[b] = 1 + level[a];
              q.push(b);
            }
          }
          ind = edges[ind].spre;
        }
      }
      if (level[n] == -1) {
        break;
      }
      pt = head;
      while (1) {
        int x = dfs(1, INF);
        if (x == 0) {
          break;
        }
        ret += x;
      }
    }
    return ret;
  }

};

int main() {
  freopen ("maxflow.in", "r", stdin);
  freopen ("maxflow.out", "w", stdout);
  int n, m;
  scanf("%d %d", &n, &m);
  flow f;
  f.init(n);
  for (int i = 1; i <= m; i++) {
    int x, y, z;
    scanf("%d %d %d", &x, &y, &z);
    f.add(x, y, z);
  }
  printf("%d\n", f.get());

}