LUA 排序算法和性能分析[6]:归并排序算法

选择排序算法

时间开销:短

稳定性:

复杂度:


math.randomseed(os.time());

local real_print = print;
local nLine = 0;
function print(...)
    real_print(nLine, ...)
    nLine = nLine + 1;
end;

local t = {};

local function dump()
    -- print(table.concat(t, ","));
end;

for i = 1, 256 do
    table.insert(t, math.random(i), i);
end;

function table_sort()
    table.sort(t);
    dump();
end;

-- table_sort() -- 0.3

-- 冒泡排序
function bubble_sort()
    print("冒泡排序")
    local n = #t;
    for j = 1, n - 1 do
        for i = 1, n - j do
            if t[i] > t[i+1] then
                t[i], t[i+1] = t[i+1], t[i];
                dump()
            end;
        end;
    end;
    dump();
end;

-- bubble_sort(); -- 5.7

-- 选择排序
function select_sort()
    print("选择排序")
    local n = #t;
    for i = 0, n - 2 do
        local min = i;
        for j = i + 1, n - 1 do
            if t[min+1] > t[j+1] then
                min = j;
            end;
        end;
        if (min ~= i) then
            t[min+1], t[i+1] = t[i+1], t[min+1];
            dump();
        end;
    end;
    dump();
end;

-- select_sort() -- 3.4

-- 快速排序
function quick_sort()
    print("快速排序")
    local function sort(left, right)
        if left >= right then
            return ;
        end;
        local i     = left;
        local j     = right;
        local key   = t[left];
        while (i < j) do
            while i < j and key <= t[j] do
                j = j - 1;
            end;
            t[i] =  t[j];
            dump()
            while i < j and key >= t[i] do
                i = i + 1;
            end;
            t[j] = t[i];
            dump()
        end;
        t[i] = key;
        dump()
        sort(left, i - 1);
        sort(i + 1, right);
    end;
    sort(1, #t)
end;

-- quick_sort() -- 0.4


function insert_sort()
    print("插入排序")
    local temp;
    for i = 2, #t do
        temp = t[i];
        j = i - 1;
        --与已排序的数逐一比较,大于temp时,该数移后
        while( (j > 0) and (t[j]>temp)) do

            t[j+1] = t[j];
            j = j - 1;
        end;
        if( j ~= i - 1) then
            t[j+1] = temp;
        end
        dump()
    end
end;

-- insert_sort() -- 4.7s


-- 归并排序
function merge_sort()
    local function merge(nStart, nMid, nEnd)
        local tempArr = {};
        local m,n,k = nStart, nMid+1, 0;

        while( m <= nMid  and n <= nEnd) do
            if t[1+m] > t[1+n] then
                tempArr[k+1] = t[1+n];
                n = n + 1;
                k = k + 1;
            else
                tempArr[k+1] = t[1+m];
                k = k + 1;
                m = m + 1;
            end
        end;
        while n < nEnd + 1 do
            tempArr[k+1] = t[1+n];
            k = k + 1;
            n = n + 1;
        end;
        while m < nMid + 1 do
            tempArr[k+1] = t[1+m];
            k = k + 1;
            m = m + 1;
        end;
        for m = nStart, nEnd do
            t[1+m] = tempArr[m + 1 - nStart];
        end;
        dump()
    end;

    local function MergeSort(nStart, nEnd)
        if nStart < nEnd then
            local nMid = math.floor((nStart + nEnd) / 2);
            MergeSort(nStart, nMid);
            MergeSort(nMid + 1, nEnd);
            merge(nStart, nMid, nEnd);
        end;
    end;

    MergeSort(0, #t-1);
end;

-- merge_sort();
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