travelling_salesman_using_bit_manipulation.cpp File Reference

Implementation to [Travelling Salesman problem using bit-masking] (https://www.geeksforgeeks.org/travelling-salesman-problem-set-1/) More...

#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iostream>
#include <limits>
#include <vector>

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Namespaces
namespace	bit_manipulation
	for assert
namespace	travellingSalesman_bitmanipulation
	Functions for the Travelling Salesman Bitmask implementation.

Functions
std::uint64_t	bit_manipulation::travelling_salesman_using_bit_manipulation::travelling_salesman_using_bit_manipulation (std::vector< std::vector< uint32_t > > dist, std::uint64_t setOfCities, std::uint64_t city, std::uint64_t n, std::vector< std::vector< uint32_t > > &dp)
	The function implements travellingSalesman using bitmanipulation.
static void	test ()
	Self-test implementations.
int	main ()
	Main function.

Detailed Description

Implementation to [Travelling Salesman problem using bit-masking] (https://www.geeksforgeeks.org/travelling-salesman-problem-set-1/)

Given the distance/cost(as and adjacency matrix) between each city/node to the other city/node , the problem is to find the shortest possible route that visits every city exactly once and returns to the starting point or we can say the minimum cost of whole tour.

Explanation: INPUT -> You are given with a adjacency matrix A = {} which contains the distance between two cities/node.

OUTPUT -> Minimum cost of whole tour from starting point

Worst Case Time Complexity: O(n^2 * 2^n) Space complexity: O(n)

Author

Utkarsh Yadav

Function Documentation

main()

int main

(

void

)

Main function.

Returns

0 on exit

           {
    test();  // run self-test implementations
    return 0;
}

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test()

static void test ( )

static

Self-test implementations.

Returns

void

                   {
    // 1st test-case
    std::vector<std::vector<uint32_t>> dist = {
        {0, 20, 42, 35}, {20, 0, 30, 34}, {42, 30, 0, 12}, {35, 34, 12, 0}};
    uint32_t V = dist.size();
    std::vector<std::vector<uint32_t>> dp(1 << V, std::vector<uint32_t>(V, -1));
    assert(bit_manipulation::travelling_salesman_using_bit_manipulation::
               travelling_salesman_using_bit_manipulation(dist, 1, 0, V, dp) ==
           97);
    std::cout << "1st test-case: passed!"
              << "\n";
 
    // 2nd test-case
    dist = {{0, 5, 10, 15}, {5, 0, 20, 30}, {10, 20, 0, 35}, {15, 30, 35, 0}};
    V = dist.size();
    std::vector<std::vector<uint32_t>> dp1(1 << V,
                                           std::vector<uint32_t>(V, -1));
    assert(bit_manipulation::travelling_salesman_using_bit_manipulation::
               travelling_salesman_using_bit_manipulation(dist, 1, 0, V, dp1) ==
           75);
    std::cout << "2nd test-case: passed!"
              << "\n";
    // 3rd test-case
    dist = {{0, 10, 15, 20}, {10, 0, 35, 25}, {15, 35, 0, 30}, {20, 25, 30, 0}};
    V = dist.size();
    std::vector<std::vector<uint32_t>> dp2(1 << V,
                                           std::vector<uint32_t>(V, -1));
    assert(bit_manipulation::travelling_salesman_using_bit_manipulation::
               travelling_salesman_using_bit_manipulation(dist, 1, 0, V, dp2) ==
           80);
 
    std::cout << "3rd test-case: passed!"
              << "\n";
}

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travelling_salesman_using_bit_manipulation()

std::uint64_t bit_manipulation::travelling_salesman_using_bit_manipulation::travelling_salesman_using_bit_manipulation	(	std::vector< std::vector< uint32_t > >	dist,
		std::uint64_t	setOfCities,
		std::uint64_t	city,
		std::uint64_t	n,
		std::vector< std::vector< uint32_t > > &	dp )

The function implements travellingSalesman using bitmanipulation.

Parameters

dist	is the cost to reach between two cities/nodes
setOfCitites	represents the city in bit form.\
city	is taken to track the current city movement.
n	is the no of citys .
dp	vector is used to keep a record of state to avoid the recomputation.

Returns

minimum cost of traversing whole nodes/cities from starting point back to starting point

{
    // base case;
    if (setOfCities == (1 << n) - 1) {  // we have covered all the cities
        return dist[city][0];  // return the cost from the current city to the
                               // original city.
    }
 
    if (dp[setOfCities][city] != -1) {
        return dp[setOfCities][city];
    }
    // otherwise try all possible options
    uint64_t ans = 2147483647;
    for (int choice = 0; choice < n; choice++) {
        // check if the city is visited or not.
        if ((setOfCities & (1 << choice)) ==
            0) {  // this means that this perticular city is not visited.
            std::uint64_t subProb =
                dist[city][choice] +
                travelling_salesman_using_bit_manipulation(
                    dist, setOfCities | (1 << choice), choice, n, dp);
            // Here we are doing a recursive call to tsp with the updated set of
            // city/node and choice which tells that where we are currently.
            ans = std::min(ans, subProb);
        }
    }
    dp[setOfCities][city] = ans;
    return ans;
}

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