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我正在尝试实现一个利用 A* 算法的 4x4 滑块拼图求解器。尽管试图以尽可能简洁的方式编写代码，但代码中出现了一个段错误，它指向将指针推送到std::priority_queue实例的尝试失败。这是我的调试尝试后的完整代码，我不知道如何将其切割成一个工作测试用例：

#include <iostream>
#include <iomanip>

#include <cstring>
#include <cmath>

#include <vector>
#include <set>
#include <queue>

#include <functional>

#include <ctime>
#include <cstdlib>

using namespace std;

const char GOAL_STATE[] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,0};

class Puzzle
{
protected:
    char puzzle[16];

    int index(char searched) const
    {
        for(int i=0; i<16; i++)
        {
            if (puzzle[i]==searched)
                return i;
        }
        return -1;
    }

public:

    Puzzle(const char init[16] = NULL)
    {
        if(init!=NULL)
        {
            memcpy(puzzle, init, sizeof(char)*16);
        }
        else
        {
            memcpy(puzzle, GOAL_STATE, sizeof(char)*16);
        }
    }

    void show() const
    {
        for(int i=0; i<4; i++)
        {
            for(int j=0; j<4; j++)
            {
                cout << setw(3) << (int)puzzle[i*4+j] << " ";
            }
            cout << endl;
        }
    }

    bool move(int m_pos)
    {
        int b_pos = index(0);
        int b_x = b_pos / 4;
        int b_y = b_pos % 4;
        int x = m_pos / 4;
        int y = m_pos % 4;
        if (m_pos < 16 && (
                    (x == b_x && (y == b_y + 1 || y == b_y - 1)) ||
                    (y == b_y && (x == b_x + 1 || x == b_x - 1))
                )
            )
        {
            char tmp = puzzle[m_pos];
            puzzle[m_pos] = puzzle[b_pos];
            puzzle[b_pos] = tmp;
            return true;
        }
        else
            return false;
    }

    int count_correct() const
    {
        int ret = 0;
        for(int i=0; i<16; i++)
            if ((i<15 && (puzzle[i])==i+1) || (i==15 && puzzle[i]==0))
                ret++;
        return ret;
    }

    vector<int> possible_moves() const
    {
        vector<int> ret;
        int b_pos = index(0);
        int b_x = b_pos / 4;
        int b_y = b_pos % 4;
        ret.push_back(b_y * 4 + b_x - 1);
        ret.push_back((b_y - 1) * 4 + b_x);
        if (b_x<3)
            ret.push_back(b_y * 4 + b_x + 1);
        if (b_y<3)
            ret.push_back((b_y + 1) * 4 + b_x);
        return ret;
    }

};

class AStarPuzzle : public Puzzle
{
    int H;
    int f;

public:

    int tried;

    AStarPuzzle* previous;

    AStarPuzzle(const char init[16] = NULL,
            int _f = 0, int _tried = 0, AStarPuzzle* _previous = NULL) : Puzzle(init)
    {
        f = _f;
        tried = _tried;
        previous = _previous;
    }

    AStarPuzzle (const AStarPuzzle& old) : Puzzle(old.puzzle)
    {
        f = old.f;
        tried = old.tried;
        previous = old.previous;
    }

    double heur() const
    {
        double ret = 0.0;
        for (int goalIndex = 0 ; goalIndex<16; goalIndex++)
        {
            int tileIndex = index( GOAL_STATE[goalIndex] );
            ret += abs((double)((goalIndex % 4) - (tileIndex % 4)));
            ret += abs(floor(goalIndex / 4.0) - floor(tileIndex / 4.0));

        }

        return 0.1*f + max(ret, (double)count_correct());
    }

    bool operator<(const AStarPuzzle& other) const
    {
        return heur()>other.heur();
    }

    int get_f()
    {
        return f;
    }

    void increase_f()
    {
        f++;
    }

    AStarPuzzle operator=(const AStarPuzzle& rhs)
    {
        cout << "STUB: AStarPuzzle::operator=" << endl;
    }

    ~AStarPuzzle()
    {
        cout << "STUB: AStarPuzzle::~AStarPuzzle" << endl;
    }


    void operator delete(void *p)
    {
        cout << "Attempting to delete AStarPuzzle?" << endl;
    }

};


struct CompareHeuristics : public std::binary_function<AStarPuzzle*, AStarPuzzle*, bool >
{
    bool operator()(AStarPuzzle* lhs, AStarPuzzle* rhs) const
    {
        return lhs->heur() > rhs->heur();
    }
};

vector<int> retracePath(AStarPuzzle* c)
{
    vector<int> ret;
    while (c->previous!=NULL)
    {
        c = c->previous;
        ret.push_back(c->tried);
    }
    return ret;
}

vector<int> aStar(AStarPuzzle* current)
{
    set<AStarPuzzle*> openList;
    set<AStarPuzzle*> closedList;
    std::priority_queue<AStarPuzzle*, std::vector<AStarPuzzle*>, CompareHeuristics> openHeap;

    int max_corr = 0;
    int min_step = 0;


    openList.insert(current);
    openHeap.push(current);
    while (openList.size()!=0)
    {
        current = openHeap.top();
        cout << "An iteration. heur()==" << current->heur()  << endl;
        current->show();
        openHeap.top();
        if (current->count_correct() == 16)
        {
            //return vector<int>();
            return retracePath(current);
        }
        openList.erase(current);
        closedList.insert(current);
        vector<int> directions = current->possible_moves();
        for(unsigned int i=0; i<directions.size(); i++)
        {
            AStarPuzzle* tile = new AStarPuzzle(*current);
            tile->move(directions[i]);
            tile->increase_f();

            if (closedList.count(tile)==0)
            {
                int corr = tile->count_correct();
                int f = tile->get_f();
                if (corr > max_corr or (corr == max_corr && f < min_step))
                {
                    max_corr = corr;
                    min_step = f;
                    cout << corr << "," << f << endl;
                }
                tile->previous = current;
                if (openList.count(tile)==0)
                {
                    openList.insert(tile);
                    openHeap.push(tile);
                }
            }

        }
    }


    return vector<int>();
}

int main(int argc, char **argv) {

    char shuffled[16];
    memcpy(shuffled, GOAL_STATE, sizeof(char)*16);
    srand(time(0));
    for (int i=0; i<16; i++) {
        int r = i + (rand() % (16-i));
        char temp = shuffled[i];
        shuffled[i] = shuffled[r];
        shuffled[r] = temp;
    }

    shuffled = {0, 3, 7, 5, 9, 12 , 13 , 11, 8, 6 , 14, 4 , 15, 2 , 10 , 1 };

    AStarPuzzle* p = new AStarPuzzle(shuffled);
    p->show();
    aStar(p);

    return 0;
}

和 gdb 输出：

> gdb ./si-proj2cpp
GNU gdb (GDB) 7.0.1-debian
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/d33tah/workspace/si-proj2cpp/Debug/si-proj2cpp...done.
(gdb) r
Starting program: /home/d33tah/workspace/si-proj2cpp/Debug/si-proj2cpp
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
An iteration. heur()==44
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
An iteration. heur()==44
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
An iteration. heur()==44
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
An iteration. heur()==44
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1

Program received signal SIGSEGV, Segmentation fault.
0xb7dab5fc in _int_free (av=<value optimized out>, p=0x80502b0) at malloc.c:4957
4957    malloc.c: No such file or directory.
        in malloc.c
Current language:  auto
The current source language is "auto; currently c".
(gdb) bt
#0  0xb7dab5fc in _int_free (av=<value optimized out>, p=0x80502b0) at malloc.c:4957
#1  0xb7dae8ad in *__GI___libc_free (mem=0x80502b8) at malloc.c:3739
#2  0xb7f86701 in operator delete(void*) () from /usr/lib/libstdc++.so.6
#3  0x0804b97b in __gnu_cxx::new_allocator<AStarPuzzle*>::deallocate (this=0xbffff564, __p=0x80502b8) at /usr/include/c++/4.4/ext/new_allocator.h:95
#4  0x0804ab4b in std::_Vector_base<AStarPuzzle*, std::allocator<AStarPuzzle*> >::_M_deallocate (this=0xbffff564, __p=0x80502b8, __n=16)
    at /usr/include/c++/4.4/bits/stl_vector.h:146
#5  0x0804b2a9 in std::vector<AStarPuzzle*, std::allocator<AStarPuzzle*> >::_M_insert_aux (this=0xbffff564, __position=..., __x=@0xbffff554)
    at /usr/include/c++/4.4/bits/vector.tcc:361
#6  0x0804a5cf in std::vector<AStarPuzzle*, std::allocator<AStarPuzzle*> >::push_back (this=0xbffff564, __x=@0xbffff554) at /usr/include/c++/4.4/bits/stl_vector.h:741
#7  0x08049bbb in std::priority_queue<AStarPuzzle*, std::vector<AStarPuzzle*, std::allocator<AStarPuzzle*> >, CompareHeuristics>::push (this=0xbffff564, __x=@0xbffff554)
    at /usr/include/c++/4.4/bits/stl_queue.h:511
#8  0x08049054 in aStar (current=0x8050008) at ../main.cpp:248
#9  0x08049273 in main (argc=1, argv=0xbffff704) at ../main.cpp:275

正如有人建议的那样，我使用 valgrind 来看看会发生什么：

> valgrind ./si-proj2cpp
==26655== Memcheck, a memory error detector
==26655== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==26655== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==26655== Command: ./si-proj2cpp
==26655==
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
An iteration. heur()==44
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
==26655== Invalid read of size 1
==26655==    at 0x804950E: Puzzle::move(int) (main.cpp:74)
==26655==    by 0x8048F3A: aStar(AStarPuzzle*) (main.cpp:231)
==26655==    by 0x8049272: main (main.cpp:275)
==26655==  Address 0x42ca1ef is 1 bytes before a block of size 32 alloc'd
==26655==    at 0x402471C: operator new(unsigned int) (vg_replace_malloc.c:255)
==26655==    by 0x8048EF6: aStar(AStarPuzzle*) (main.cpp:230)
==26655==    by 0x8049272: main (main.cpp:275)
==26655==
==26655== Invalid write of size 1
==26655==    at 0x8049525: Puzzle::move(int) (main.cpp:75)
==26655==    by 0x8048F3A: aStar(AStarPuzzle*) (main.cpp:231)
==26655==    by 0x8049272: main (main.cpp:275)
==26655==  Address 0x42ca1ef is 1 bytes before a block of size 32 alloc'd
==26655==    at 0x402471C: operator new(unsigned int) (vg_replace_malloc.c:255)
==26655==    by 0x8048EF6: aStar(AStarPuzzle*) (main.cpp:230)
==26655==    by 0x8049272: main (main.cpp:275)
==26655==
An iteration. heur()==44
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
An iteration. heur()==44
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
(...looks like an infinite loop, so I'm stopping the program with ctr+c)
  0   3   7   5
  9  12  13  11
  8   6  14   4
 15   2  10   1
^CAn iteration. heur()==44
==26655==
==26655== HEAP SUMMARY:
==26655==     in use at exit: 17,076 bytes in 579 blocks
==26655==   total heap usage: 805 allocs, 226 frees, 21,156 bytes allocated
==26655==
==26655== LEAK SUMMARY:
==26655==    definitely lost: 0 bytes in 0 blocks
==26655==    indirectly lost: 0 bytes in 0 blocks
==26655==      possibly lost: 0 bytes in 0 blocks
==26655==    still reachable: 17,076 bytes in 579 blocks
==26655==         suppressed: 0 bytes in 0 blocks
==26655== Rerun with --leak-check=full to see details of leaked memory
==26655==
==26655== For counts of detected and suppressed errors, rerun with: -v
==26655== ERROR SUMMARY: 288 errors from 2 contexts (suppressed: 19 from 8)
4

3 回答 3

1

您忘记在AStarPuzzle::operator=. 然后，Ideone 不会报告 segfault，而是超时。也许你应该在更进一步之前更正无限循环......另外，你正在使用intin Puzzle::movefor m_pos，并且你没有检查负值。改为使用unsigned int。

编辑：在 Visual C++ 2010 上测试，没有段错误，无限循环。您应该检查您是否使用了正确的运行时。

于 2013-03-03T14:10:13.620 回答
1

你在这里做有符号的 int 算术

vector<int> possible_moves() const
{
    vector<int> ret;
    int b_pos = index(0);
    int b_x = b_pos / 4;
    int b_y = b_pos % 4;
    ret.push_back(b_y * 4 + b_x - 1);
    ret.push_back((b_y - 1) * 4 + b_x);
    if (b_x<3)
        ret.push_back(b_y * 4 + b_x + 1);
    if (b_y<3)
        ret.push_back((b_y + 1) * 4 + b_x);
    return ret;
}

然后你用它作为地址：

    vector<int> directions = current->possible_moves();
    for(unsigned int i=0; i<directions.size(); i++)
    {
        AStarPuzzle* tile = new AStarPuzzle(*current);
        tile->move(directions[i]);    // <<------ here, line 231
        tile->increase_f();

用 s替换您的int索引，unsigned int根据编译器的要求更改代码，然后看看会发生什么。

于 2013-03-03T14:20:54.740 回答
0

这个问题实际上与内存无关，它是 - 正如@Synxis 指出的那样 - 负 m_pos 被传递给 Puzzle::move。发生这种情况的原因是 possible_moves() 没有考虑 0 块位于 (0,0) 中的情况 - 修复 possible_moves 有所帮助。另一个错误与 x 和 y 相反，并且 openHeap.top() 被调用两次而不是 openHeap.top()、openHeap.pop()。

于 2013-03-03T14:23:03.473 回答