Task: Floyd-Warshall algorithm


C++: #include <iostream>
#include <vector>
#include <sstream>

void print(std::vector<std::vector<double>> dist, std::vector<std::vector<int>> next) {
  std::cout << "(pair, dist, path)" << std::endl;
  const auto size = std::size(next);
  for (auto i = 0; i < size; ++i) {
    for (auto j = 0; j < size; ++j) {
      if (i != j) {
        auto u = i + 1;
        auto v = j + 1;
        std::cout << "(" << u << " -> " << v << ", " << dist[i][j]
          << ", ";
        std::stringstream path;
        path << u;
        do {
          u = next[u - 1][v - 1];
          path << " -> " << u;
        } while (u != v);
        std::cout << path.str() << ")" << std::endl;
      }
    }
  }
}

void solve(std::vector<std::vector<int>> w_s, const int num_vertices) {
  std::vector<std::vector<double>> dist(num_vertices);
  for (auto& dim : dist) {
    for (auto i = 0; i < num_vertices; ++i) {
      dim.push_back(INT_MAX);
    }
  }
  for (auto& w : w_s) {
    dist[w[0] - 1][w[1] - 1] = w[2];
  }
  std::vector<std::vector<int>> next(num_vertices);
  for (auto i = 0; i < num_vertices; ++i) {
    for (auto j = 0; j < num_vertices; ++j) {
      next[i].push_back(0);
    }
    for (auto j = 0; j < num_vertices; ++j) {
      if (i != j) {
        next[i][j] = j + 1;
      }
    }
  }
  for (auto k = 0; k < num_vertices; ++k) {
    for (auto i = 0; i < num_vertices; ++i) {
      for (auto j = 0; j < num_vertices; ++j) {
        if (dist[i][j] > dist[i][k] + dist[k][j]) {
          dist[i][j] = dist[i][k] + dist[k][j];
          next[i][j] = next[i][k];
        }
      }
    }
  }
  print(dist, next);
}

int main() {
  std::vector<std::vector<int>> w = {
    { 1, 3, -2 },
    { 2, 1, 4 },
    { 2, 3, 3 },
    { 3, 4, 2 },
    { 4, 2, -1 },
  };
  int num_vertices = 4;
  solve(w, num_vertices);
  std::cin.ignore();
  std::cin.get();
  return 0;
}




Java: import static java.lang.String.format;
import java.util.Arrays;

public class FloydWarshall {

    public static void main(String[] args) {
        int[][] weights = {{1, 3, -2}, {2, 1, 4}, {2, 3, 3}, {3, 4, 2}, {4, 2, -1}};
        int numVertices = 4;

        floydWarshall(weights, numVertices);
    }

    static void floydWarshall(int[][] weights, int numVertices) {

        double[][] dist = new double[numVertices][numVertices];
        for (double[] row : dist)
            Arrays.fill(row, Double.POSITIVE_INFINITY);

        for (int[] w : weights)
            dist[w[0] - 1][w[1] - 1] = w[2];

        int[][] next = new int[numVertices][numVertices];
        for (int i = 0; i < next.length; i++) {
            for (int j = 0; j < next.length; j++)
                if (i != j)
                    next[i][j] = j + 1;
        }

        for (int k = 0; k < numVertices; k++)
            for (int i = 0; i < numVertices; i++)
                for (int j = 0; j < numVertices; j++)
                    if (dist[i][k] + dist[k][j] < dist[i][j]) {
                        dist[i][j] = dist[i][k] + dist[k][j];
                        next[i][j] = next[i][k];
                    }

        printResult(dist, next);
    }

    static void printResult(double[][] dist, int[][] next) {
        System.out.println("pair     dist    path");
        for (int i = 0; i < next.length; i++) {
            for (int j = 0; j < next.length; j++) {
                if (i != j) {
                    int u = i + 1;
                    int v = j + 1;
                    String path = format("%d -> %d    %2d     %s", u, v,
                            (int) dist[i][j], u);
                    do {
                        u = next[u - 1][v - 1];
                        path += " -> " + u;
                    } while (u != v);
                    System.out.println(path);
                }
            }
        }
    }
}