c++ - C++中的简单探路者

Question

我正在开发一个简单的探路者。我有一个基于网格的小 map 。
'1' 是一层
'0'是一堵墙
“G”是目标之一

特点:
- 没有对角线移动
- 路径成本总是等于 1
- 可以有很多目标

我的完整代码:

#include <vector>
#include <iostream>
#include <map>
#include <algorithm>

using namespace std;

const int MapWidth = 10, MapHeight = 10;
//       Y pos      X pos
char Map[MapHeight][MapWidth] = {
    { '1', '1', 'G', '1', '1', '1', '1', '1', '1', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '1', '1', '1' },
    { '1', '1', '0', '1', '1', '1', '1', '1', '0', 'G' },
    { '1', '1', '0', '0', '1', '1', '1', '1', '0', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '1', '1', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '0', '0', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '0', '1', '1' },
    { '1', '1', '1', '0', '0', '1', '1', '0', '1', '1' },
    { '1', '1', '0', '0', '0', '1', '1', '0', '0', '0' },
    { '1', '1', '1', 'G', '0', '1', '1', '1', '1', '1' }
};

struct Pos
{
    int X;
    int Y;
};

bool PosIsUsed(vector <Pos> Position, int Y, int X)
{
    for (vector <Pos>::iterator it = Position.begin(); it != Position.end(); ++it)
    {
        if (it->X == X && it->Y == Y)
        {
            return true;
        }
    }
    return false;
}

void SearchNext(int Y, int X, vector <Pos> Position)
{
    Pos NewStep = { X, Y };
    Position.push_back(NewStep);
    //North
    if (Y >= 1 && !PosIsUsed(Position, Y - 1, X))
    {
        vector <Pos> NewPosition = Position;
        switch (Map[Y - 1][X])
        {
        case '1':
            SearchNext(Y - 1, X, NewPosition);
            break;
        case 'G':
            printf("Found!\n");
            break;
        }
    }
    //East
    if (X + 1 < MapWidth && !PosIsUsed(Position, Y, X + 1))
    {
        vector <Pos> NewPosition = Position;
        switch (Map[Y][X + 1])
        {
        case '1':
            SearchNext(Y, X + 1, NewPosition);
            break;
        case 'G':
            printf("Found!\n");
            break;
        }
    }
    //Soth
    if (Y + 1 < MapHeight && !PosIsUsed(Position, Y + 1, X))
    {
        vector <Pos> NewPosition = Position;
        switch (Map[Y + 1][X])
        {
        case '1':
            SearchNext(Y + 1, X, NewPosition);
            break;
        case 'G':
            printf("Found!\n");
            break;
        }
    }
    //West
    if (X >= 1 && !PosIsUsed(Position, Y, X - 1))
    {
        vector <Pos> NewPosition = Position;
        switch (Map[Y][X - 1])
        {
        case '1':
            SearchNext(Y, X - 1, NewPosition);
            break;
        case 'G':
            printf("Found!\n");
            break;
        }
    }

}

int main()
{
    vector <Pos> Pos;
    SearchNext(9, 9, Pos); //We start here (Pos [9][9])
    printf("End\n");
    system("PAUSE");
    return 0;
}

有问题。它永远不会结束。你能告诉我，我做错了什么吗？

编辑:

我在 SearchNext 函数中切换了 X 和 Y 参数的顺序。进行此更改后，程序会显示无穷大“Found!”。

工作代码(不是我的):

#include <vector>
#include <iostream>
#include <map>
#include <algorithm>
#include <string>

using namespace std;


const char FLOOR = '1' ;
const char WALL  = '0' ;
const char GOAL  = 'G' ;

const int MapWidth = 10, MapHeight = 10;
//       Y pos      X pos
char Map[MapHeight][MapWidth] = {
    { '1', '1', 'G', '1', '1', '1', '1', '1', '1', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '1', '1', '1' },
    { '1', '1', '0', '1', '1', '1', '1', '1', '0', 'G' },
    { '1', '1', '0', '0', '1', '1', '1', '1', '0', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '1', '1', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '0', '0', '1' },
    { '1', '1', '1', '1', '1', '1', '1', '0', '1', '1' },
    { '1', '1', '1', '0', '0', '1', '1', '0', '1', '1' },
    { '1', '1', '0', '0', '0', '1', '1', '0', '0', '0' },
    { '1', '1', '1', 'G', '0', '1', '1', '1', '1', '1' }
};

struct Pos
{
    short x,y;
    Pos operator + ( Pos p ) const { return Pos(x+p.x,y+p.y); }
    bool operator < ( Pos p ) const { return ( y==p.y ) ? (x<p.x) : (y<p.y) ; }
    bool operator != ( Pos p ) const { return ( y!=p.y ) || (x!=p.x) ; }
    Pos(short x=0,short y=0) : x(x), y(y) {}
};

bool valid(Pos p) { return p.x>=0 && p.x<MapWidth && p.y>=0 && p.y<MapHeight; }

enum Dir { d_beg, d_up=d_beg, d_rg, d_dn, d_lf, d_end };

Pos deltas[d_end] = { {0,-1}, {+1,0}, {0,+1}, {-1,0} };

Dir& operator ++ ( Dir& d ) { d = (Dir) ( 1+(int)d ) ; return d; }

Dir other(Dir d)
{
    switch(d)
    {
    case d_up: return d_dn;
    case d_rg: return d_lf;
    case d_dn: return d_up;
    case d_lf: return d_rg;
    default: return d_end;
    }
}

struct SearchMapItem
{
    bool traversble;
    bool goal;
    bool visited;
    int cost_here;
    Dir came_from;
    bool paths[d_end];
};

map<Pos,SearchMapItem> search_map;
typedef map<Pos,SearchMapItem>::iterator SMII;

void MakeMap()
{
    search_map.clear();
    Pos p;
    for(p.y=0;p.y<MapHeight;++p.y) for(p.x=0;p.x<MapWidth;++p.x) 
    {
        SearchMapItem smi;
        smi.visited = false;
        smi.cost_here = -1;
        smi.came_from = d_end;
        if( Map[p.y][p.x] == WALL )
        {
            smi.traversble = false;
        }
        else if( Map[p.y][p.x] == GOAL )
        {
            smi.traversble = true;
            smi.goal = true;
        }
        else if( Map[p.y][p.x] == FLOOR )
        {
            smi.traversble = true;
            smi.goal = false;
            for( Dir d = d_beg; d != d_end; ++d )
            {
                Pos p2 = p + deltas[d];
                smi.paths[d] = valid(p2) && (Map[p2.y][p2.x] != WALL) ;
            }
        }
        search_map[p] = smi;
    }
}

void FindGoalFrom( Pos start )
{
    vector<SMII> found;

    {
        SMII smii = search_map.find(start);

        if(smii==search_map.end()) { cout << "starting outside map\n"; return; }
        if(smii->second.goal) { cout << "already at target\n"; return; }
        if(!smii->second.traversble) { cout << "starting in a wall\n"; return; }

        smii->second.visited = true;
        smii->second.cost_here = 0;
        found.push_back(smii);
    }

    int cost_so_far = 0;
    bool did_find = false;

    while(!did_find)
    {

        vector<SMII> candidates;

        for( SMII smii : found )
        {
            for( Dir d = d_beg; d != d_end; ++d )
            {
                if( ! smii->second.paths[d] ) continue;
                Pos p = smii->first + deltas[d];
                if(!valid(p)) continue;
                SMII cand = search_map.find(p);
                if(cand==search_map.end()) continue;
                if(cand->second.visited) continue;
                cand->second.came_from=d;
                candidates.push_back(cand);
            }
        }

        ++cost_so_far;

        if( candidates.empty() ) break;

        for( SMII smii : candidates )
        {
            smii->second.visited = true;
            smii->second.cost_here = cost_so_far;
            found.push_back(smii);
            if( smii->second.goal ) { did_find = true; break; }
        }

    }

    if( ! did_find ) { cout << "no goal reachable\n"; return; }

    SMII pos = found.back();

    vector<Dir> path;

    while( pos->first != start )
    {
        Dir d = pos->second.came_from;
        path.push_back(d);
        Pos p = pos->first + deltas[ other(d) ];
        pos = search_map.find(p);
    }

    for( auto itr = path.rbegin(); itr != path.rend(); ++itr )
    {
        const char* dir_names[] = { "Up", "Right", "Down", "Left" } ;
        cout << "Walk " << dir_names[*itr] << endl;
    }
    cout << "Then you are at goal in total " << to_string(cost_so_far) << " steps" << endl;
}

int main()
{
    MakeMap();

    FindGoalFrom( Pos(5,9) );

    cout << "\ndone\n";
}

Answer 1

您在对 SearchNext 的递归调用中切换 X 和 Y 的顺序。

通常，您可以在调试器中或通过添加跟踪输出来分析这些类型的问题。您会在第二次调用 SearchNext 时发现问题:“哈，为什么当我从 Y 中减去 1 时 X 等于 8？”。