ch05 exercises

exercises/ch05/ex5_4.lua

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+local function polynomial(coefs, x)
+    local sum = 0
+    for i = 1, #coefs do
+        sum = sum + coefs[i] * x^i
+    end
+
+    return sum
+end
+
+local function table_str(t)
+    local str = "{ "
+    for _, v in pairs(t) do
+        str = str + v + ", "
+    end
+
+    str = str + "}"
+end
+
+local function test(coefs, x, should_be)
+    local res = polynomial(coefs, x)
+    if res ~= should_be then
+        print(
+            ("Test failed. Should have been %f, was %f. coefs: %s, x: %f"):format(should_be, res, table_str(coefs), x)
+        )
+    else
+        print("Test passed.")
+    end
+end
+
+test({1, 2, 3}, 2, 1 * 2^1 + 2 * 2^2 + 3 * 2^3)

exercises/ch05/ex5_6.lua

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+local function is_sequence(t)
+    local prev_k = 0
+    for k, _ in pairs(t) do
+        if type(k) ~= "number" or k ~= prev_k + 1 then
+            return false
+        end
+
+        prev_k = prev_k + 1
+    end
+
+    return true
+end
+
+local function table_str(t)
+    local str = "{"
+    for k, v in pairs(t) do
+        if type(k) == "string" then
+            k = '"' .. k .. '"'
+        end
+        str = ("%s [%s] = %s,"):format(str, k, v)
+    end
+
+    str = str .. " }"
+
+    return str
+end
+
+local function test(t)
+    print(("%s: %q"):format(table_str(t), is_sequence(t)))
+end
+
+test({ 1, 2, 3, word = "a word", [10] = 999 })
+test({ 1, 2, 3 })
+test({ [1.0] = 1, [2] = 2 })
+test({ [1.1] = 1, [2] = 2 })

exercises/ch05/ex5_7.lua

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+local function insert_into(insert, into, pos)
+    local insert_i = 0
+    for into_i = pos, #into + #insert do
+        local new_into_i = into_i + #insert
+        into[new_into_i] = into[into_i]
+        into[into_i] = insert[insert_i]
+        insert_i = insert_i + 1
+    end
+end
+
+local function table_str(t)
+    local str = "{"
+    for _, v in pairs(t) do
+        if type(v) == "string" then
+            v = '"' .. v .. '"'
+        end
+        str = ("%s %s,"):format(str, v)
+    end
+
+    str = str .. " }"
+
+    return str
+end
+
+local function test(insert, into, pos)
+    print("------------------------------")
+    print(("pos: %d"):format(pos))
+    print(("insert: %s"):format(table_str(insert)))
+    print(("before: %s"):format(table_str(into)))
+    insert_into(insert, into, pos)
+    print(("after: %s"):format(table_str(into)))
+    print("------------------------------")
+end
+
+test({5, 6, 7}, {1, 2, 3, 10, 11}, 4)
+
+test({"a", "b", "c"}, { "a", "b", "c", "d", "e" }, 5)
+
+test({"brave", "new"}, {"hello", "world"}, 2)

exercises/ch05/ex5_8.lua

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+local function concat(strs)
+    local res = ""
+    for i = 1, #strs do
+        res = res .. strs[i]
+    end
+
+    return res
+end
+
+local function random_str()
+    return tostring(math.random(100000, 999999))
+end
+
+local strs = {}
+for i = 1, 200000 do
+    strs[i] = random_str()
+end
+
+local time_start = os.clock()
+concat(strs)
+local own_concat_time = os.clock() - time_start
+
+print("Own concat time: " .. own_concat_time)
+
+time_start = os.clock()
+_ = table.concat(strs)
+local table_concat_time = os.clock() - time_start
+
+print("table.concat time: " .. table_concat_time)
+
+print(("table.concat was %f%s faster"):format(own_concat_time / table_concat_time * 100, "%"))