[人工智能]八数码（A*）

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/Pecony/article/details/83037783

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <iostream>

using namespace std;

int goal[9] = { 1,2,3,8,0,4,7,6,5 };//goal为棋盘的目标布局
int intermediate[9];//中间过程棋盘

struct Board
{
	int a[9];
	int depth;
	int fn;
	int prenode;  //前一次移动方式
};

struct LinkList
{
	Board node;
	LinkList *parent;
	LinkList *pre;
	LinkList *next;
	LinkList *path; //专门记录路径
};


void SetBoard(int current[], int b[]);//更新纪录八数码的状态
int Weight(int a[]);
LinkList *NewNode(LinkList *nowmin, int depth, int direction);//生成一个新节点的函数
LinkList *AddNode(LinkList *Openhead, LinkList *node);
LinkList *MinNode(LinkList *Openhead);

int main()
{
	int depth = 0;
	//int initial[9] = {2, 8, 3, 1, 6, 4, 7, 0, 5};
	int initial[9] = {2, 8, 3, 1, 0, 4, 7, 6, 5};
    int i;
	LinkList *Open = new LinkList;
	LinkList *node = new LinkList;

    //初始化
    for (int i = 0;i <= 8;i++)
        Open->node.a[initial[i]] = i;
    Open->node.depth = depth;
	Open->node.prenode = 0;
	Open->node.fn = depth + Weight(initial);
	Open->next = NULL;
	Open->pre = NULL;
	Open->parent = NULL;

	while (Open)
	{
		node = MinNode(Open);  //求具有最小启发值的移动

		SetBoard(intermediate, node->node.a);   //写当前过程棋盘intermediate

		if (!Weight(intermediate))//已经排好
			break;

        //从Open表中删除当前最小节点 因为已扩充完毕
        if (node != Open)
		{
			node->pre->next = node->next;
			node->next->pre = node->pre;
		}
		else
		{
			if (Open->next)
			{
				Open = Open->next;
				Open->pre = NULL;
			}
			else Open = NULL;
		}
		//判断棋子是否回到之前状态 node当前移动方式
		if (node->node.a[0] - 1 >= 0 && node->node.prenode != 2)//左移一个仍在棋盘中 且之前不是右移操作
			Open = AddNode(Open, NewNode(node, depth, 1));
		if (node->node.a[0] + 1 <= 8 && node->node.prenode != 1)
			Open = AddNode(Open, NewNode(node, depth, 2));
		if (node->node.a[0] - 3 >= 0 && node->node.prenode != 4)
			Open = AddNode(Open, NewNode(node, depth, 3));
		if (node->node.a[0] + 3 <= 8 && node->node.prenode != 3)
			Open = AddNode(Open, NewNode(node, depth, 4));
		depth++;
	}//end_while

    if (Open)//输出解
	{
		node->path = NULL;
		while (node->parent)           //回溯父节点，生成路径
		{
			node->parent->path = node;//path是专门用来记录路径的 从下向上回溯记录
			node = node->parent;
		}
		int j = 0;
		while (node->path)//此时node是输出的头
		{
			SetBoard(intermediate, node->node.a);//每一步进行更新
			printf("第%d步：\n", j + 1);
			for (i = 0; i < 9;i++)
            {
                printf("%d  ", intermediate[i]);
                if(!((i + 1) % 3))
                    cout << endl;
            }
			node = node->path;//从上到下输出
			j++;
		}
		SetBoard(intermediate, node->node.a);
		printf("第%d步：\n", j + 1);
        for (i = 0; i < 9;i++)
        {
            printf("%d  ", intermediate[i]);
            if(!((i + 1) % 3))
                cout << endl;
        }
	}
    else
		printf("无法求解！");
}


//更新纪录
void SetBoard(int intermediate[], int b[])
{
	for (int i = 0;i <= 8;i++)
        intermediate[b[i]] = i;
}
int Weight(int a[])   //不在位棋子数
{
    int c = 0;
    int b = 0;
	for (int i = 0;i <= 8;i++)
        for (int j = 0;j <= 8;j++)
        {
             if (a[i] == goal[j])
            {
                if (goal[j] != 0 && i != j) //  找到当前棋子与目标棋子 i!=j代表未放置在目标位置
                {
                      c += abs(i%3-j%3)+abs((i- i%3)/3-(j- j%3)/3);
                }

            }
        }
	return c;

}

LinkList *NewNode(LinkList *nowmin, int depth, int direction)
{
	LinkList *temp = new LinkList;
	for (int i = 0;i <= 8;i++)  //拷贝
		temp->node.a[i] = nowmin->node.a[i];

	switch (direction)
	{
	case 1: //向左移
	{
		temp->node.a[0]--;
		temp->node.a[intermediate[temp->node.a[0]]]++;
		break;
	}
	case 2://向右移
	{
		temp->node.a[0]++;
		temp->node.a[intermediate[temp->node.a[0]]]--;
		break;
	}//上下移动均为3的关系
	case 3:
	{
		temp->node.a[0] -= 3;
		temp->node.a[intermediate[temp->node.a[0]]] += 3;  //向上移
		break;
	}
	case 4:
	{
		temp->node.a[0] += 3;
		temp->node.a[intermediate[temp->node.a[0]]] -= 3;   //向下移
		break;
	}
	}
    temp->node.depth = depth + 1;//结点扩展后 深度加一
	SetBoard(intermediate, temp->node.a);//更新
	temp->node.fn = temp->node.depth + Weight(intermediate);
	temp->node.prenode = direction;//prenode记录移动的方向
	temp->parent = nowmin;

	return temp;
}
LinkList *AddNode(LinkList *Openhead, LinkList *node)   //加入Open表
{
	LinkList *h;
	h = Openhead;
	Openhead = node;
	Openhead->next = h;
	Openhead->pre = NULL;
	if (h)
		h->pre = Openhead;
	return Openhead;
}
//求启发值最小的结点
LinkList *MinNode(LinkList *Openhead)
{
	LinkList *minnode, *nextnode;
	minnode = Openhead;
	nextnode = Openhead;
	while (nextnode)    //执行到倒数第二个结束
	{
		if (minnode->node.fn > nextnode->node.fn)
			minnode = nextnode;
		nextnode = nextnode->next;
	}
	return minnode;
}