started ch05

exercises/ch04/ex4_9.lua

@@ -0,0 +1,52 @@
+local function remove(str, start, _end)
+    -- print(start, _end, str:sub(start, start), str:sub(_end, _end))
+    local start_part = str:sub(1, start - 1)
+    local end_part = str:sub(_end + 1, -1)
+    return start_part .. end_part
+end
+
+local function remove_patterns(str, pattern)
+    while true do
+        local rem_start, rem_end, _ = str:find(pattern)
+        if rem_start == nil then
+            break
+        end
+        -- print(str, pattern, rem_start, rem_end)
+        str = remove(str, rem_start, rem_end)
+        -- print(str)
+    end
+
+    return str
+end
+
+local function ispali(str)
+    str = str:lower()
+
+    -- format
+    str = remove_patterns(str, "%s")
+    str = remove_patterns(str, "%p")
+
+    for i = 1, utf8.len(str) do
+        local idx = utf8.offset(str, i)
+        local idx_rev = utf8.offset(str, -i)
+        local ch_code = utf8.codepoint(str, idx)
+        local ch_code_rev = utf8.codepoint(str, idx_rev)
+        if ch_code ~= ch_code_rev then
+            return false
+        end
+    end
+
+    return true
+end
+
+local function test(str)
+    print(("%s: %q"):format(str, ispali(str)))
+end
+
+test("step ön nö pets")
+test("bänänä")
+
+print()
+
+test("step. ön nö   pets!")
+test("bänänä??")