遗传算法求f(x)=x1^2+x2^2最大值，其中0<=x1,x2<=7。

//this program uses SGA to calculate the maximum value of f(x) = x1^2 + x2^2
#include <iostream>
#include <ctime>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#define LENGTH 3
using namespace std;

class chromosome
{
public:
	int x1,x2;
	int value;
	double fitness;
	void assign(int a,int b)
	{
		x1 = a;
		x2 = b;
		cal_value();
	}
	void cal_value()
	{
		value = x1 << LENGTH;
		value |= x2;
	}
	void cal_fitness()
	{
		fitness = x1*x1 + x2*x2;
	}
};
double total_fitness = 0;
vector<chromosome> population[2];
vector<chromosome> temp;
int cop_counter = 0;
int selector = 0;
int and1 = ((1 << LENGTH) - 1) << LENGTH;
int and2 = (1 << LENGTH) - 1;
int variation_percent = 2;

int random(int end)
{
	return rand() % (end + 1);
}

//选择
void select_population()
{
	int counter = 0;
	int new_sel = (selector + 1) % 2;
	population[new_sel].clear();
	while (counter <= 3)
	{
		int pos = population[selector].size() - 1;
		int r = random(total_fitness);
		int end = population[selector][0].fitness;
		for (int i = 1;i < (int)population[selector].size();i++)
			if (r <= end)
			{
				pos = i - 1;
				break;
			}
			else
				end += population[selector][i].fitness;
		population[new_sel].push_back(population[selector][pos]);
		counter++;
	}
}

//两个染色体进行交配
void cop(chromosome &temp1, chromosome &temp2)
{
	chromosome new1, new2;
	int pos = random(LENGTH * 2 - 2);//0..LENGTH * 2 - 2 (end position)
	int v1 = temp1.value;
	int v2 = temp2.value;
	int length = LENGTH * 2;
	int num1 = ((1 << pos) - 1) << (length - pos);
	int num2 = ((1 << (length - pos)) - 1);
	int part11 = v1 & num1;
	int part12 = v1 & num2;
	int part21 = v2 & num1;
	int part22 = v2 & num2;
	int new_v1 = part11 | part22;
	int new_v2 = part21 | part12;
	new1.assign((new_v1 & and1) >> LENGTH, new_v1 & and2);
	new2.assign((new_v2 & and1) >> LENGTH, new_v2 & and2);
	temp.push_back(new1);
	temp.push_back(new2);
}

//种群内随机进行两两交配
void copulation()
{
	chromosome temp1,temp2;
	int remainder = 4;
	int r1,r2;
	int new_sel = (selector + 1) % 2;

	cop_counter = 0;
	while (remainder)
	{
		r1 = random(remainder-1);
		temp1 = population[new_sel][r1];
		population[new_sel].erase(population[new_sel].begin() + r1);
		remainder--;
		r2 = random(remainder-1);
		temp2 = population[new_sel][r2];
		population[new_sel].erase(population[new_sel].begin() + r2);
		remainder--;
		cop(temp1,temp2);
	}
	population[new_sel] = temp;
	temp.clear();
}

//变异
void variation()
{
	int new_sel = (selector + 1) % 2;
	for (int i = 0;i < (int)population[new_sel].size();i++)
	{
		int rand = random(99) + 1;
		if (rand <= 2)
		{
			int pos = random(LENGTH * 2 - 1) + 1;
			int num = 1 << (LENGTH * 2 - pos);
			population[new_sel][i].value ^= num;
			population[new_sel][i].x1 = (population[new_sel][i].value & and1) >> LENGTH;
			population[new_sel][i].x2 = population[new_sel][i].value & and2;
		}
	}
}

//更新适应度
void update_fitness()
{
	total_fitness = 0;
	for (int i = 0;i < (int)population[selector].size();i++)
	{
		population[selector][i].cal_fitness();
		total_fitness += population[selector][i].fitness;
	}
}

bool cmp(chromosome a,chromosome b)
{
	return a.fitness < b.fitness;
}

//initial population: 1 6, 2 4, 3 5, 4 1
void init()
{
	srand((unsigned)time(NULL));
	chromosome chr;
	chr.assign(1,6);
	population[0].push_back(chr);
	chr.assign(2,4);
	population[0].push_back(chr);
	chr.assign(3,5);
	population[0].push_back(chr);
	chr.assign(4,1);
	population[0].push_back(chr);
}

//debug
/*int b[100];
char str[100];
int bcounter=0;
void tobinary(int x)
{
	memset(b,0,sizeof(b));
	bcounter=0;
	while (x>0)
	{
		b[bcounter++]=x%2;
		x/=2;
	}
	int i;
	for (i = 0;i < 6;i++)
		str[i]=b[5-i]+'0';
	str[i]='\0';
}*/

int main()
{
	int counter = 0;
	init();
	int maxn = 0;
	int maxvalue;
	while (counter <= 1000)
	{
		update_fitness();
		sort(population[selector].begin(),population[selector].end(),cmp);
		if (population[selector][population[selector].size() - 1].fitness > maxn)
		{
			maxn = population[selector][population[selector].size() - 1].fitness;
			maxvalue = population[selector][population[selector].size() - 1].value;
		}
		select_population();
		copulation();
		variation();
		selector = (selector + 1) % 2;
		counter++;
	}
	printf("x1:%d x2:%d\n",(maxvalue&and1)>>LENGTH,maxvalue&and2);
}