A*是一種很常見的游戲?qū)ぢ匪惴ā?/p>

長久以來沾鳄，我一直覺得A*是一種高大上的算法施流，因?yàn)槁牶芏嗳苏f起此算法响疚，然而，江湖一張紙瞪醋，戳穿不值一毛錢忿晕，思路其實(shí)很簡(jiǎn)單通過估值函數(shù)決定下一步走向

估值函數(shù)

• 決定整個(gè)算法的效率，以及準(zhǔn)確率银受。
• 可以根據(jù)實(shí)際需求践盼，使用不同的估值函數(shù)鸦采。

實(shí)現(xiàn)

#pragma once

#include "base.h"
#include "math.h"
#include "priority_queue.h"

class AStar {
public:
    struct Box {
        MATH Vec2 parent;
        MATH Vec2 self;
        int G, H;
        int F() const
        {
            return G + H;
        }

        Box()
        { }

        explicit Box(const MATH Vec2 & pt1, const MATH Vec2 & pt2)
            : parent(pt1)
            , self(pt2)
        { }

        explicit Box(const MATH Vec2 & pt1, const MATH Vec2 & pt2, int g, int h)
            : parent(pt1)
            , self(pt2)
            , G(g)
            , H(h)
        { }

        bool operator==(const MATH Vec2 & point) const
        {
            return MATH equal(self, point);
        }

        bool operator<(const Box & other) const
        {
            return F() > other.F();
        }
    };

    using NextFunc = STD function<void(const MATH Vec2 &)>;
    using TestFunc = STD function<bool(const MATH Vec2 &)>;
public:
    AStar()
    { }

    ~AStar()
    { }

    bool IsFinish()
    {
        return _openList.empty() || MATH equal(_end, _openList.top().self);
    }

    const MATH Vec2 & GetQueryBeg() const
    {
        return _beg;
    }

    const MATH Vec2 & GetQueryEnd() const
    {
        return _end;
    }

    void SetQueryPoint(const MATH Vec2 & beg, const MATH Vec2 & end)
    {
        _beg = beg;
        _end = end;
        _closeList.clear();
        _openList = priority_queue<Box>();
        _openList.emplace(beg, beg, 0, 0);
    }

    bool GetQueryPath(STD vector<MATH Vec2> & path)
    {
        if (!MATH equal(_end, _closeList.back().self))
        {
            return false;
        }
        auto parent = _closeList.back().self;
        for (; !_closeList.empty(); _closeList.pop_back())
        {
            if (MATH equal(parent, _closeList.back().self))
            {
                path.push_back(_closeList.back().self);
                parent = _closeList.back().parent;
            }
        }
        return true;
    }

    void SetTestFunc(const TestFunc & func)
    {
        _testFunc = func;
    }

    void SetNextFunc(const NextFunc & func)
    {
        _nextFunc = func;
    }

    bool QueryNext()
    {
        static const MATH Vec2 s_offset[] = {
            { 0, -1 },{ 1, 0 },{ 0, 1 },{ -1, 0 },          //  上，右咕幻，下渔伯，左。
            //{ 1, -1 },{ 1, 1 },{ -1, 1 },{ -1,-1 },           //  右上肄程，右下锣吼，左下，左上蓝厌。
        };
        
        if (!MATH equal(_end, _openList.top().self))
        {
            auto top = _openList.top();
            _closeList.push_back(top);
            _nextFunc(top.self);
            _openList.pop();
            for (auto &offset : s_offset)
            {
                CheckPoint(top, MATH add(top.self, offset));
            }
        }

        if (!_openList.empty() && MATH equal(_end, _openList.top().self))
        {
            _closeList.push_back(_openList.top());
            _nextFunc(_openList.top().self);
        }

        return IsFinish();
    }

private:
    void CheckPoint(const Box & from, const MATH Vec2 & to)
    {
        if (Test(to))
        {
            _openList.emplace(from.self, to, from.G + 1, Distance(to));
        }
    }

    int Distance(const MATH Vec2 & point)
    {
        return (int)(STD abs(point.x - _end.x) + STD abs(point.y - _end.y));
    }

    bool Test(const MATH Vec2 & point)
    {
        return _testFunc(point)
            && STD find(_openList.begin(), _openList.end(), point) == _openList.end()
            && STD find(_closeList.begin(), _closeList.end(), point) == _closeList.end();
    }

private:
    MATH Vec2 _beg;
    MATH Vec2 _end;
    NextFunc _nextFunc;
    TestFunc _testFunc;
    priority_queue<Box> _openList;
    STD vector<Box> _closeList;

private:
    AStar(const AStar &) = delete;
    AStar(AStar &&) = delete;
    AStar operator=(const AStar &) = delete;
    AStar operator=(AStar &&) = delete;

};

效果

A*尋路

DEMO下載