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Travelling Salesman solution in CPP #738

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203 changes: 203 additions & 0 deletions Traveling-Salesman.cpp
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// Traveling Salesman - Nishant Giri

#include <bits/stdc++.h>
#include <limits.h>
using namespace std;

// Number of cities in TSP
#define V 5

// Names of the cities
#define GENES ABCDE

// Starting Node Value
#define START 0

// Initial population size for the algorithm
#define POP_SIZE 10

// Structure of a GNOME
// string defines the path traversed
// by the salesman while the fitness value
// of the path is stored in an integer

struct individual {
string gnome;
int fitness;
};

// Function to return a random number
// from start and end
int rand_num(int start, int end)
{
int r = end - start;
int rnum = start + rand() % r;
return rnum;
}

// Function to check if the character
// has already occurred in the string
bool repeat(string s, char ch)
{
for (int i = 0; i < s.size(); i++) {
if (s[i] == ch)
return true;
}
return false;
}

// Function to return a mutated GNOME
// Mutated GNOME is a string
// with a random interchange
// of two genes to create variation in species
string mutatedGene(string gnome)
{
while (true) {
int r = rand_num(1, V);
int r1 = rand_num(1, V);
if (r1 != r) {
char temp = gnome[r];
gnome[r] = gnome[r1];
gnome[r1] = temp;
break;
}
}
return gnome;
}

// Function to return a valid GNOME string
// required to create the population
string create_gnome()
{
string gnome = "0";
while (true) {
if (gnome.size() == V) {
gnome += gnome[0];
break;
}
int temp = rand_num(1, V);
if (!repeat(gnome, (char)(temp + 48)))
gnome += (char)(temp + 48);
}
return gnome;
}

// Function to return the fitness value of a gnome.
// The fitness value is the path length
// of the path represented by the GNOME.
int cal_fitness(string gnome)
{
int map[V][V] = { { 0, 2, INT_MAX, 12, 5 },
{ 2, 0, 4, 8, INT_MAX },
{ INT_MAX, 4, 0, 3, 3 },
{ 12, 8, 3, 0, 10 },
{ 5, INT_MAX, 3, 10, 0 } };
int f = 0;
for (int i = 0; i < gnome.size() - 1; i++) {
if (map[gnome[i] - 48][gnome[i + 1] - 48] == INT_MAX)
return INT_MAX;
f += map[gnome[i] - 48][gnome[i + 1] - 48];
}
return f;
}

// Function to return the updated value
// of the cooling element.
int cooldown(int temp)
{
return (90 * temp) / 100;
}

// Comparator for GNOME struct.
bool lessthan(struct individual t1,
struct individual t2)
{
return t1.fitness < t2.fitness;
}

// Utility function for TSP problem.
void TSPUtil(int map[V][V])
{
// Generation Number
int gen = 1;
// Number of Gene Iterations
int gen_thres = 5;

vector<struct individual> population;
struct individual temp;

// Populating the GNOME pool.
for (int i = 0; i < POP_SIZE; i++) {
temp.gnome = create_gnome();
temp.fitness = cal_fitness(temp.gnome);
population.push_back(temp);
}

cout << "\nInitial population: " << endl
<< "GNOME FITNESS VALUE\n";
for (int i = 0; i < POP_SIZE; i++)
cout << population[i].gnome << " "
<< population[i].fitness << endl;
cout << "\n";

bool found = false;
int temperature = 10000;

// Iteration to perform
// population crossing and gene mutation.
while (temperature > 1000 && gen <= gen_thres) {
sort(population.begin(), population.end(), lessthan);
cout << "\nCurrent temp: " << temperature << "\n";
vector<struct individual> new_population;

for (int i = 0; i < POP_SIZE; i++) {
struct individual p1 = population[i];

while (true) {
string new_g = mutatedGene(p1.gnome);
struct individual new_gnome;
new_gnome.gnome = new_g;
new_gnome.fitness = cal_fitness(new_gnome.gnome);

if (new_gnome.fitness <= population[i].fitness) {
new_population.push_back(new_gnome);
break;
}
else {

// Accepting the rejected children at
// a possible probablity above threshold.
float prob = pow(2.7,
-1 * ((float)(new_gnome.fitness
- population[i].fitness)
/ temperature));
if (prob > 0.5) {
new_population.push_back(new_gnome);
break;
}
}
}
}

temperature = cooldown(temperature);
population = new_population;
cout << "Generation " << gen << " \n";
cout << "GNOME FITNESS VALUE\n";

for (int i = 0; i < POP_SIZE; i++)
cout << population[i].gnome << " "
<< population[i].fitness << endl;
gen++;
}
}

int main()
{

int map[V][V] = { { 0, 2, INT_MAX, 12, 5 },
{ 2, 0, 4, 8, INT_MAX },
{ INT_MAX, 4, 0, 3, 3 },
{ 12, 8, 3, 0, 10 },
{ 5, INT_MAX, 3, 10, 0 } };
TSPUtil(map);
}