Qt：实现git中diff的功能

在 Git 中，有四种 diff 算法，即 Myers、Minimal、Patience 和 Histogram，用于获取位于两个不同 commit 中的两个相同文件的差异。

Myers算法实现参考：

Myers'Diff之贪婪算法_myers算法-CSDN博客

Git Diff 算法详解：Myers Diff Algorithm-腾讯云开发者社区-腾讯云 (tencent.com)

Myers差分算法的理解、实现、可视化 - Oto_G - 博客园 (cnblogs.com)

最后找到一个c++可用的代码如下，在Myers函数中传入两个需要比较的文档内容。

#include <QDir>
#include <QVariantMap>
#include <QVariantList>
#include <QStringList>
#include <QList>
#include <QDebug>

namespace ScriptManagerWebNew {
enum MoveType {
    MoveType_None,
    MoveType_Down,
    MoveType_Right,
    MoveType_Diagonal
};
struct Point {
    Point(int x, int y) {
        this->x = x;
        this->y = y;
    }

    bool operator== (const Point& pt) const {
        return this->x == pt.x && this->y == pt.y;
    }

    bool operator!= (const Point& pt) const {
        return this->x != pt.x || this->y != pt.y;
    }

    MoveType operator >(const Point& pt2) {
        if (this->x == pt2.x && this->y + 1 == pt2.y) {
            return MoveType_Down;
        }
        else if (this->y == pt2.y && this->x + 1 == pt2.x) {
            return MoveType_Right;
        }
        else if (this->x + 1 == pt2.x && this->y + 1 == pt2.y) {
            return MoveType_Diagonal;
        }

        return MoveType_None;
    }

    int x = 0;
    int y = 0;
};


QString Myers(QString formerText, QString currentText)
{
    const auto lines = formerText.split("\n");
    const auto lines2 = currentText.split("\n");
    auto n = lines.size();
    auto m = lines2.size();
    std::vector<std::map<int, int>> Xlist;
    //只存储x坐标,y可以由k=x-y算出
    std::map<int,int> X;
    //假设起始点(0,-1)
    X[1] = 0;
    bool go_ahead = true;
    //步数d
    //从0开始，因为d=0时，也可能沿对角线前进
    for (int d = 0; d <= n + m && go_ahead; d++) {
        //k-lines: k has odd or even values according to an odd or even d
        for (int k = -d; k <= d; k = k + 2) {
            //判断该从(d-1,k-1)向右走，还是从(d-1,k+1)向下走
            //当k!=d && k!=-d时, 可以从X[k + 1]向下走, 或者X[k - 1]向右走
            //具体怎么选择，判断x值：选择x大的,保证删除操作优于添加操作
            bool down = (k == -d || (k != d && X[k - 1] < X[k + 1]));
            int kPrev = down ? k + 1 : k - 1;
            //起始位置
            int xStart = X[kPrev];
            int yStart = xStart - kPrev;
            //中间位置
            int xTmp = down ? xStart : xStart + 1;
            int yTmp = xTmp - k;
            //此次move后的位置
            int xEnd = xTmp;
            int yEnd = yTmp;
            //判断能否总对角线(moving through a diagonal is free)
            while (xEnd < n && yEnd < m && lines[xEnd] == lines2[yEnd]) {
                ++xEnd;
                ++yEnd;
            }
            X[k] = xEnd;

            //到终点,找到了最短路线
            if (xEnd >= n && yEnd >= m) {
                go_ahead = false;
                break;
            }
        }

        Xlist.push_back(X);
    }

    //回退，从终点到起点，找出路线
    std::vector<Point> path; //move的路线
    Point pt(lines.length(), lines2.length());
    path.push_back(pt);
    for (int d = Xlist.size() - 1; pt.x > 0 || pt.y > 0; --d) {
        auto X = Xlist[d];
        int k = pt.x - pt.y;

        //结束位置
        int xEnd = X[k];
        int yEnd = pt.x - k;
        //结束位置前是否走的对角线
        while (xEnd > 0 && yEnd > 0 && xEnd <= n && yEnd <= m && lines[xEnd-1] == lines2[yEnd-1]) {
            --xEnd;
            --yEnd;
            path.push_back(Point(xEnd, yEnd));
        }

        //down可以确定上一步的k线，对角线上的移动不影响d和k
        //并且,Xlist[d][k-1] == Xlist[d-1][k-1]; Xlist[d][k+1] == Xlist[d-1][k+1]
        bool down = (k == -d || (k != d && X[k - 1] < X[k + 1]));
        int kPrev = down ? k + 1 : k - 1;

        //起始位置
        int xStart = X[kPrev];
        int yStart = xStart - kPrev;

        中间位置
        //int xTmp = down ? xStart : xStart + 1;
        //int yTmp = xTmp - k;

        path.push_back(Point(xStart, yStart));

        pt.x = xStart;
        pt.y = yStart;
    }

    path.pop_back();//path第一个点是假设的起点(0,-1);

    //文字描述path代表的操作
    QString stream;
//    std::stringstream stream;
    if (path.size() >= 2) {
        int size = path.size();
        for (int i = size - 2; i >= 0; --i) {
            Point prev_point = path[i+1];
            MoveType type = prev_point>(path[i]);
            switch (type) {
            case MoveType_Right: {
                stream.append("-" + lines[prev_point.x]+"\n");
                break;
            }
            case MoveType_Down: {
                stream.append( "+" + lines2[prev_point.y]+"\n");
                break;
            }
            case MoveType_Diagonal: {
                stream.append(lines[prev_point.x]+"\n");
                break;
            }
            }
        }
    }
//    std::cout << "最短编辑路线如下：" << std::endl;
//    std::cout << stream.str();
//    std::string input;
//    std::cin >> input;
    return stream;
}