八数码问题使用HashTable优化查找后的版本
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在《双向广度优先搜索算法框架及八数码问题例程》一文中，给出了使用双向广度优先搜索算法解决八数码问题的一个
简单版本，查找都是线性的，没有优化。这里给出使用HashTable优化后的版本！
/*
?* Author: puresky
?* Date: 2010.01.12
?* Purpose: solve EIGTH NUMBER problem!
?*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXN 10000
#define SWAP(a, b) {char t = a; a = b; b = t;}
typedef struct _Node Node;
struct _Node
{
??????? char tile[10]; // represent the tile as a string ending with '\0'
??????? char pos;?? // the position of 'x'
??????? char dir;? //the moving direction of 'x'
??????? int parent; //index of parent node
};
int head[2], tail[2];
Node queue[2][MAXN];// two queues for double directoin BFS
//shift of moving up, down, left ,right
int shift[4][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
//for output direction!
char dir[4][2] = {{'u', 'd'}, {'d', 'u'}, {'l', 'r'}, {'r', 'l'}};
//test case
char start[10] = "23415x768";
char end[10] = "12345678x";
/*=================hash table start=========================================*/
#define HASH_TABLE_MAX_SIZE 10000
typedef struct HashNode_Struct HashNode;
struct HashNode_Struct
{
??????? char* sKey;
??????? int nValue;
??????? HashNode* pNext;
};
HashNode* ht[2][HASH_TABLE_MAX_SIZE];//hash table data strcutrue
//initialize hash table
void hash_table_init(HashNode *hashTable[])
{
??????? memset(hashTable, 0, sizeof(HashNode*) * HASH_TABLE_MAX_SIZE);
}
//string hash function
unsigned int hash_table_hash_str(const char* skey)
{
??????? const signed char *p = (const signed char*)skey;
??????? unsigned int h = *p;
??????? if(h)
??????? {
??????????????? for(p += 1; *p != '\0'; ++p)
??????????????????????? h = (h << 5) - h + *p;
??????? }
??????? return h;
}
//insert key-value into hash table
void hash_table_insert(HashNode *hashTable[], char* skey, int nvalue)
{
??????? unsigned int pos = hash_table_hash_str(skey) % HASH_TABLE_MAX_SIZE;
??????? HashNode* pHead =? hashTable[pos];
??????? while(pHead)
??????? {
??????????????? if(strcmp(pHead->sKey, skey) == 0)
??????????????? {
??????????????????????? printf("%s already exists!\n", skey);
??????????????????????? return ;
??????????????? }
??????????????? pHead = pHead->pNext;
??????? }
??????? HashNode* pNewNode = (HashNode*)malloc(sizeof(HashNode));
??????? memset(pNewNode, 0, sizeof(HashNode));
??????? pNewNode->sKey = skey;
??????? pNewNode->nValue = nvalue;
??????? pNewNode->pNext = hashTable[pos];
??????? hashTable[pos] = pNewNode;
}
//lookup a key in the hash table
HashNode* hash_table_lookup(HashNode *hashTable[], const char* skey)
{
??????? unsigned int pos = hash_table_hash_str(skey) % HASH_TABLE_MAX_SIZE;
??????? if(hashTable[pos])
??????? {
??????????????? HashNode* pHead = hashTable[pos];
??????????????? while(pHead)
??????????????? {
??????????????????????? if(strcmp(skey, pHead->sKey) == 0)
??????????????????????????????? return pHead;
??????????????????????? pHead = pHead->pNext;
??????????????? }
??????? }
??????? return NULL;
}
//free the memory of the hash table
void hash_table_release(HashNode *hashTable[])
{
??????? int i;
??????? for(i = 0; i < HASH_TABLE_MAX_SIZE; ++i)
??????? {
??????????????? if(hashTable[i])
??????????????? {
??????????????????????? HashNode* pHead = hashTable[i];
??????????????????????? while(pHead)
??????????????????????? {
??????????????????????????????? HashNode* pTemp = pHead;
??????????????????????????????? pHead = pHead->pNext;
??????????????????????????????? if(pTemp)
??????????????????????????????? {
??????????????????????????????????????? free(pTemp);
??????????????????????????????? }
??????????????????????? }
??????????????? }
??????? }
}
/* ===============================hash table end=========================*/
//read a tile 3 by 3
void readtile()
{
??????? int i;
??????? char temp[10];
??????? for(i = 0; i < 9; ++i)
??????? {
??????????????? scanf("%s", temp);
??????????????? start[i] = temp[0];
??????? }
??????? start[9] = '\0';
}
//print result
void print_backward(int i)
{
??????? if(queue[0][i].parent != -1)
??????? {
??????????????? print_backward(queue[0][i].parent);
??????????????? printf("%c", queue[0][i].dir);
??????? }
}
void print_forward(int j)
{
??????? if(queue[1][j].parent != -1)
??????? {
??????????????? printf("%c", queue[1][j].dir);
??????????????? print_forward(queue[1][j].parent);
??????? }
}
void print_result(int i, int j)
{
??????? //printf("%d,%d\n", i, j);
??????? print_backward(i);
??????? print_forward(j);
??????? printf("\n");
}
//init the queue
void init(int qi, const char* state)
{
??????? strcpy(queue[qi][0].tile, state);
??????? queue[qi][0].pos = strchr(state, 'x') - state;
??????? queue[qi][0].parent = -1;
??????? head[qi] = tail[qi]? = 0;
}
//check if there are duplicates in the queue
//time comlexity:O(n)
//We can optimise this function using HashTable
int isduplicate(int qi)
{
??????? if(hash_table_lookup(ht[qi], queue[qi][tail[qi]].tile))
??????? {
??????????????? return 1;
??????? }
??????? return 0;
}
//check if the current node is in another queue!
//time comlexity:O(n)
//We can optimise this function using HashTable
int isintersect(int qi)
{
??????? HashNode* hn = hash_table_lookup(ht[1 - qi], queue[qi][tail[qi]].tile);
??????? if(hn)
??????? {
??????????????? return hn->nValue;
??????? }
??????? return -1;
}
//expand nodes
int expand(int qi)
{
??????? int i, x, y, r;
??????? Node* p = &(queue[qi][head[qi]]);
??????? head[qi]++;
??????? for(i = 0; i < 4; ++i)
??????? {
??????????????? x = p->pos / 3 + shift[i][0];
??????????????? y = p->pos % 3 + shift[i][1];
??????????????? if(x >= 0 && x <= 2 && y >= 0 && y <= 2)
??????????????? {
??????????????????????? tail[qi]++;
??????????????????????? Node* pNew = &(queue[qi][tail[qi]]);
??????????????????????? strcpy(pNew->tile, p->tile);
??????????????????????? SWAP(pNew->tile[ 3 * x + y], pNew->tile[p->pos]);
??????????????????????? pNew->pos = 3 * x + y;
??????????????????????? pNew->parent = head[qi] - 1;
??????????????????????? pNew->dir = dir[i][qi];
??????????????????????? if(isduplicate(qi))
??????????????????????? {
??????????????????????????????? tail[qi]--;
??????????????????????? }
??????????????????????? else
??????????????????????? {
??????????????????????????????? if((r = isintersect(qi)) != -1)
??????????????????????????????? {
??????????????????????????????????????? if(qi == 1)
??????????????????????????????????????? {
??????????????????????????????????????????????? print_result(r, tail[qi]);
??????????????????????????????????????? }
??????????????????????????????????????? else
??????????????????????????????????????? {
??????????????????????????????????????????????? print_result(tail[qi], r);
??????????????????????????????????????? }
??????????????????????????????????????? return 1;
??????????????????????????????? }
??????????????????????????????? hash_table_insert(ht[qi], pNew->tile, tail[qi]);
??????????????????????? }
??????????????? }
??????? }
??????? return 0;
}
//call expand to generate queues
int solve()
{
??????? init(0, start);
??????? init(1, end);
???????
??????? while(head[0] <= tail[0] && head[1] <= tail[1])
??????? {
??????????????? //expand the shorter queue firstly
??????????????? if(tail[0] - head[0] >= tail[1] - head[1])
??????????????? {
??????????????????????? if(expand(1)) return 1;
??????????????? }
??????????????? else
??????????????? {
??????????????????????? if(expand(0)) return 1;
??????????????? }
??????? }
???????
??????? while(head[0] <= tail[0]) if(expand(0)) return 1;
??????? while(head[1] <= tail[1]) if(expand(1)) return 1;
??????? return 0;
}
int main(int argc, char** argv)
{
??????? hash_table_init(ht[0]);
??????? hash_table_init(ht[1]);
??????? readtile();
??????? if(!solve())
??????? {
??????????????? printf("unsolvable\n");
??????? }
??????? hash_table_release(ht[0]);
??????? hash_table_release(ht[1]);
??????? //system("pause"); //pause
??????? return 0;
}
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