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--- Trie implementation in luajit
-- Copyright © 2019 Ashkan Kiani
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation, either version 3 of the License, or
-- (at your option) any later version.
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-- GNU General Public License for more details.
-- You should have received a copy of the GNU General Public License
-- along with this program. If not, see <http://www.gnu.org/licenses/>.
local ffi = require "ffi"
ffi.cdef [[
struct Trie {
bool is_leaf;
struct Trie* character[62];
};
void *malloc(size_t size);
void free(void *ptr);
]]
local Trie_t = ffi.typeof "struct Trie"
local Trie_ptr_t = ffi.typeof("$ *", Trie_t)
local Trie_size = ffi.sizeof(Trie_t)
local function trie_create()
local ptr = ffi.C.malloc(Trie_size)
ffi.fill(ptr, Trie_size)
return ffi.cast(Trie_ptr_t, ptr)
end
local function trie_destroy(trie)
if trie == nil then
return
end
for i = 0, 61 do
local child = trie.character[i]
if child ~= nil then
trie_destroy(child)
end
end
ffi.C.free(trie)
end
local INDEX_LOOKUP_TABLE = ffi.new "uint8_t[256]"
local CHAR_LOOKUP_TABLE = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
do
local b = string.byte
for i = 0, 255 do
if i >= b "0" and i <= b "9" then
INDEX_LOOKUP_TABLE[i] = i - b "0"
elseif i >= b "A" and i <= b "Z" then
INDEX_LOOKUP_TABLE[i] = i - b "A" + 10
elseif i >= b "a" and i <= b "z" then
INDEX_LOOKUP_TABLE[i] = i - b "a" + 10 + 26
else
INDEX_LOOKUP_TABLE[i] = 255
end
end
end
local function trie_insert(trie, value)
if trie == nil then
return false
end
local node = trie
for i = 1, #value do
local index = INDEX_LOOKUP_TABLE[value:byte(i)]
if index == 255 then
return false
end
if node.character[index] == nil then
node.character[index] = trie_create()
end
node = node.character[index]
end
node.is_leaf = true
return node, trie
end
local function trie_search(trie, value, start)
if trie == nil then
return false
end
local node = trie
for i = (start or 1), #value do
local index = INDEX_LOOKUP_TABLE[value:byte(i)]
if index == 255 then
return
end
local child = node.character[index]
if child == nil then
return false
end
node = child
end
return node.is_leaf
end
local function trie_longest_prefix(trie, value, start)
if trie == nil then
return false
end
-- insensitive = insensitive and 0x20 or 0
start = start or 1
local node = trie
local last_i = nil
for i = start, #value do
local index = INDEX_LOOKUP_TABLE[value:byte(i)]
-- local index = INDEX_LOOKUP_TABLE[bor(insensitive, value:byte(i))]
if index == 255 then
break
end
local child = node.character[index]
if child == nil then
break
end
if child.is_leaf then
last_i = i
end
node = child
end
if last_i then
-- Avoid a copy if the whole string is a match.
if start == 1 and last_i == #value then
return value
else
return value:sub(start, last_i)
end
end
end
local function trie_extend(trie, t)
assert(type(t) == "table")
for _, v in ipairs(t) do
trie_insert(trie, v)
end
end
--- Printing utilities
local function index_to_char(index)
if index < 0 or index > 61 then
return
end
return CHAR_LOOKUP_TABLE:sub(index + 1, index + 1)
end
local function trie_as_table(trie)
if trie == nil then
return nil
end
local children = {}
for i = 0, 61 do
local child = trie.character[i]
if child ~= nil then
local child_table = trie_as_table(child)
child_table.c = index_to_char(i)
table.insert(children, child_table)
end
end
return {
is_leaf = trie.is_leaf,
children = children,
}
end
local function print_trie_table(s)
local mark
if not s then
return { "nil" }
end
if s.c then
if s.is_leaf then
mark = s.c .. "*"
else
mark = s.c .. "─"
end
else
mark = "├─"
end
if #s.children == 0 then
return { mark }
end
local lines = {}
for _, child in ipairs(s.children) do
local child_lines = print_trie_table(child, thicc)
for _, child_line in ipairs(child_lines) do
table.insert(lines, child_line)
end
end
local child_count = 0
for i, line in ipairs(lines) do
local line_parts = {}
if line:match "^%w" then
child_count = child_count + 1
if i == 1 then
line_parts = { mark }
elseif i == #lines or child_count == #s.children then
line_parts = { "└─" }
else
line_parts = { "├─" }
end
else
if i == 1 then
line_parts = { mark }
elseif #s.children > 1 and child_count ~= #s.children then
line_parts = { "│ " }
else
line_parts = { " " }
end
end
table.insert(line_parts, line)
lines[i] = table.concat(line_parts)
end
return lines
end
local function trie_to_string(trie)
if trie == nil then
return "nil"
end
local as_table = trie_as_table(trie)
return table.concat(print_trie_table(as_table), "\n")
end
local Trie_mt = {
__new = function(_, init)
local trie = trie_create()
if type(init) == "table" then
trie_extend(trie, init)
end
return trie
end,
__index = {
insert = trie_insert,
search = trie_search,
longest_prefix = trie_longest_prefix,
extend = trie_extend,
},
__tostring = trie_to_string,
__gc = trie_destroy,
}
return ffi.metatype("struct Trie", Trie_mt)
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