Question

Hi
I write a program for solving 9 problem by bfs which is attached bellow.
I want to change this code in order to make it use of dfs. in my bfs I used an array and 2 pointers to simulate queue and putting successor at the end of queue each time.
I don’t know what should I do to change it to DFS.
what should I do?

#include <stdio.h>    
#include <conio.h>            
#define MAX_QUEUE_SIZE 1000            
struct State    
{    
    int table[3][3];        
};        

struct Queue    
{   
  State contents[MAX_QUEUE_SIZE];    
  int front;                                
  int count;   
};        

//prototypes of functions

int checkGoal(State curState);    
State* findChilds(State state);    
void printState(State state);       

int main()    
{    
    //number of steps    
    int nodesNumber=0;              
    //initial state    
    State s0;

    s0.table[0][0]=1;    
    s0.table[0][1]=2;    
    s0.table[0][2]=3;    
    s0.table[1][0]=4;    
    s0.table[1][1]=8;   
    s0.table[1][2]=5;    
    s0.table[2][0]=7;   
    s0.table[2][1]=9;    
    s0.table[2][2]=6;        

    Queue queue={NULL,0,0};    
    queue.contents[queue.count++]=s0;               
    //check that if the front node in queue pass the goal test finish the program    
    while(checkGoal(queue.contents[queue.front])!=1)    
    {    
        nodesNumber++;   
        //removeing front node from queue and shift front pointer to next one    
        State curState = queue.contents[queue.front++];     
        //print current state table    
        printState(curState);          
        //getting successors of current state   
        State* childStates=findChilds(curState);     
        //putting successors to queue

        for(int i=0;i<4;i++)
            queue.contents[queue.count++]=childStates[i];
    }
    printState(queue.contents[queue.front]);    
    printf("Number of Nodes Which Were Tested In BFS Tree is : %d\n",nodesNumber);      
    getch();    
    return 0;    
}      

//if even one of the cells of the table are not equal to its number correct will be false 
int checkGoal(State curState)    
{  
  int correct=1;    
  for(int i=0;i<3;i++)  
  {  
      for(int j=0;j<3;j++)   
      {
          if(curState.table[i][j]!=(i*3+j+1))
          {
              correct=0;
          }
      }
  }
  return correct;  
}    

void printState(State state)   
{
  for(int i=0;i<3;i++) {
      for(int j=0;j<3;j++)
          printf("%d ",state.table[i][j]);
      printf("\n");
  }
  printf("\n\n");
}
//return list of childs of given state 
State* findChilds(State state)
{
    State* newStates=new State[4];
    //temporary table    
    int x[3][3];    
    int a,b,counter=0;
    //creating all possible states

    for(int i=0;i<2;i++) 
    {
       for(int j=0;j<2;j++)
       {
          for(a=0;a<3;a++)
          for(int b=0;b<3;b++)

          x[a][b] = state.table[a][b];

        //rotating
            int temp = x[i][j+1]; 
            x[i][j+1] = x[i][j];
            x[i][j] = x[i+1][j];
            x[i+1][j] = x[i+1][j+1];
            x[i+1][j+1] = temp;
            State newState;

            for(a=0;a<3;a++)
                for(b=0;b<3;b++)
                    newState.table[a][b]=x[a][b];

            //putting new state in the queue
            newStates[counter++]=newState;
        }
    }
    return newStates;
}

Answer 1

BFS uses a Queue, DFS uses a stack. In your case, all you need to do is to pick the element at the back of the array instead of the front element to turn your BFS into a DFS, i.e. turn

  State curState = queue.contents[queue.front++];

into

  State curState = queue.contents[--queue.count];

and change the other parts that refer to queue.front accordingly.