【入门夯实】数组交集与差集的集合运算实现

local function intersectBad(a, b)
    local out = {}
    for _, va in ipairs(a) do
        for _, vb in ipairs(b) do
            if va == vb then
                table.insert(out, va)
            end
        end
    end
    return out
end

local function toSet(t)
    local s = {}
    for _, v in ipairs(t) do
        s[v] = true
    end
    return s
end
local function intersect(a, b)
    local sb = toSet(b)
    local out = {}
    for _, v in ipairs(a) do
        if sb[v] then
            out[#out + 1] = v
        end
    end
    return out
end
local function difference(a, b)
    local sb = toSet(b)
    local out = {}
    for _, v in ipairs(a) do
        if not sb[v] then
            out[#out + 1] = v
        end
    end
    return out
end

local function union(a, b)
    local sa = toSet(a)
    local out = {}
    for _, v in ipairs(a) do
        out[#out + 1] = v
    end
    for _, v in ipairs(b) do
        if not sa[v] then
            out[#out + 1] = v
        end
    end
    return out
end