[modified] refactored insert_sorted to get PR #18 merged

This commit is contained in:
Max Cahill 2021-04-30 11:46:51 +10:00
parent 5601d9415b
commit 826a2797c8

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@ -48,68 +48,50 @@ function tablex.unshift(t, v)
return t
end
function tablex.is_sorted(t)
local sorted = true
for i = 1, #t - 1 do
if t[i] > t[i + 1] then
sorted = false
break
end
end
return sorted
--default comparison; hoisted for clarity
--(shared with sort.lua and suggests the sorted functions below should maybe be refactored there)
local function default_less(a, b)
return a < b
end
--check if a function is sorted based on a "less" or "comes before" ordering comparison
--if any item is "less" than the item before it, we are not sorted
--(use stable_sort to )
function tablex.is_sorted(t, less)
less = less or default_less
for i = 1, #t - 1 do
if less(t[i + 1], t[i]) then
return false
end
end
return true
end
--insert to the first position before the first larger element in the table
--if this is used on an already sorted table, the table will remain sorted and not need re-sorting
--todo: make it do binary search rather than linear to improve performance
--(you can check if the table is sorted and sort if needed if you don't know)
--return the table for possible chaining
function tablex.insert_sorted(t, v, less)
local inserted = false
-- to use binary search is necessary as precondition that
-- the table is sorted
if not tablex.is_sorted(t) then
for i = 1, #t do
if less(v, t[i]) then
table.insert(t, i, v)
inserted = true
break
end
end
if not inserted then
table.insert(t, v)
end
return t
end
local l = 1
local r = #t
if r < l then
table.insert(t,v)
return t
end
while l <= r do
local mid = math.floor(l + (r - l) / 2)
if (less(v, t[mid]) or v == t[mid]) and (mid == 1 or less(t[mid - 1], v) or t[mid - 1] == v) then
table.insert(t, mid, v)
inserted = true
less = less or default_less
local low = 1
local high = #t
local match
while low <= high do
local mid = math.floor((low + high) / 2)
local mid_val = t[mid]
if less(v, mid_val) then
high = mid - 1
elseif less(mid_val, v) then
low = mid + 1
else
match = mid
break
elseif less(t[mid], v) then
l = mid + 1
elseif less(v, t[mid - 1]) then
r = mid - 1
end
end
if not inserted then
table.insert(t, l, v)
end
table.insert(t, match or low, v)
return t
end
--find the index in a sequential table that a resides at
--or nil if nothing was found
function tablex.index_of(t, a)