c++ - 8-Puzzle Solver unexpected behavior -

i working on 8-puzzle solver -using best-first search+ hamming distance(tiles out of place) heuristic- required project.

i first defined stat struct in separated cpp file looks in header file :

#ifndef stat_h_included #define stat_h_included #include <iostream>  struct stat {     int board[3][3];     int depth;     int empty[2];     int evaluation;     int operator- (stat) const; //overloading operator- return "hamming distance"     void operator= (stat);     bool operator== (stat) const;     bool operator< (stat) const; };  //used compare class set container  class comparor  //class compare between stats(default bigger) {     bool bigger;  public:     comparor(const bool& smaller=1)     {         bigger=smaller?0:1;     }     bool operator() (const stat& lhs, const stat& rhs) const     {         if (bigger) return (lhs<rhs?0:1);         else return (lhs<rhs);     } }; std::istream& operator>> (std::istream&,stat&); //to input 9-cells 1  std::ostream& operator<< (std::ostream&,stat&); //to output 9-cells 1 #endif // stat_h_included 

next main.cpp file :

#include <vector> #include <set> #include <algorithm> #include <fstream> #include "stat.h"  using namespace std;  //global variables stat start,goal,temp; int steps=0; set<stat,comparor> open; //used stats arranged -by heuristic value- , unique vector<stat> closed;  //forward declaration int solver(); inline int generate_move(char);  int main() {     ifstream cin("input.txt");      cin>>start>>goal;     start.depth=0;     start.evaluation=start-goal;     open.insert(start);     solver();     cout<<temp<<endl;     cout<<endl<<"setps reach goal = "<<steps<<endl;     return 0; }  int solver() {   set<stat,comparor>::iterator it=open.begin();   temp=*it;   if(temp==goal)     return steps;   cout<<temp<<endl;   closed.push_back(temp);   open.erase(it);    start=temp;   if(temp.empty[0]<2) //up direction     generate_move('u');   if(temp.empty[0]>0) //down direction     generate_move('d');   if(temp.empty[1]<2) //right direction     generate_move('r');   if(temp.empty[1]>0) //left direction     generate_move('l');    steps++;   solver(); }  inline int generate_move(char direction) {   int index,inverse,row,coloum;   int e0=temp.empty[0],e1=temp.empty[1];    if(direction == 'u'){index=1;inverse=0;}   else if(direction == 'd'){index=-1;inverse=0;}   else if(direction == 'r'){index=0;inverse=1;}   else if(direction == 'l'){index=0;inverse=-1;}    row=e0+index;   coloum=e1+inverse;    swap(temp.board[e0][e1],temp.board[row][coloum]); //swapping empty cell adjacent cell   if(find(closed.begin(),closed.end(),temp)!=closed.end())   {       temp=start;       return 0;   }   //changing place of empty cell new place   temp.empty[0]=row;   temp.empty[1]=coloum;    temp.depth++; //increasing depth of stat    //setting heuristic value of stat   temp.evaluation=goal-temp;   temp.evaluation+=temp.depth;    open.insert(temp);   temp=start;   return 0; } 

now when run program sample input :

2 8 3 1 6 4 7 0 5  1 2 3 8 0 4 7 6 5 

it solves puzzle , good.but every other input tried open set became empty before reaching goal despite fact there is solution puzzles.

edit: tried see stats entered open set , didn't used input below sample , got :

stats entered open :

2 8 3    2 8 3    2 0 3    0 2 3    1 2 3     1 2 3 1 6 4    1 0 4    1 8 4    1 8 4    0 8 4     8 0 4 7 0 5    7 6 5    7 6 5    7 6 5    7 6 5     7 6 5 

which steps needed solve puzzle.

stats not found in closed , didn't enter open:

2 8 3    2 8 3     2 8 3    1 2 3 1 6 4    1 4 0     0 1 4    7 8 4 0 7 5    7 6 5     7 6 5    0 6 5 

so , open set says above stats exists in open , refuse input them there no such stats in open , heuristic values of states different on open(4,4,5,5,5,5) others(6,6,5,7).

can please tell me why open refuse enter stats if exist. in advance.