String generation with genetic algorithm.

genetic.cpp

#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdlib>
#include <string>

using namespace std;

string result = "hello world!";

int closeness(const string & a) {
    int res = result.size();
    for (int i = 0; i < result.size(); i++) {
        if (result[i] != a[i]) res--;
    }
    return res;
}

bool comp(const string & a, const string & b) {
    return (closeness(a) < closeness(b));
}

int main(int, char**) {
    string alphabet = "abcdefghijklmnopqrstuvwxyz !";
    int len = alphabet.length();

    int start_size = 20;
    vector<string> population(start_size);

    for (int i = 0; i < population.size(); ++i) {
        for (int j = 0; j < result.size(); ++j) {
            population[i].push_back(alphabet[rand() % len]);
        }
    }
   
    int cnt = 0;

    while (true) {
        cnt++;

        // crossing
        for (int i = 0; i < start_size; ++i) {
            int m = rand() % population.size();
            int n = rand() % population.size();
            int pivot = rand() % (result.size() - 1);
            string new_subject = population[m].substr(0, pivot) + population[n].substr(pivot, result.size());
            population.push_back(new_subject);
        }
        // mutation
        for (int i = 0; i < population.size(); ++i) {
            if (rand() % 100 <= 5) {
                population[i][rand() % (population[i].length())] = alphabet[rand() % len];
            }
        }
        // selection
        std::sort(population.rbegin(), population.rend(), comp);
        population.erase(population.begin() + start_size, population.end());
        
        cout << population[0] << endl;

        if (closeness(population[0]) == result.size())
            break;
    }
    cout << "Generation count: " << cnt << endl;
    return 0;
}