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# Copyright (c) 2016 DeNA Co., Ltd., Ichito Nagata
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to
# deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
# sell copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
# IN THE SOFTWARE.
#
class LRUCache
def initialize(capacity)
@capacity = capacity
@head = nil
@tail = nil
@nodes = {}
raise "capacity must not be negative" if @capacity < 0
end
def set(key, value)
if ! @head
@nodes[key] = @head = @tail = [ nil, nil, key, value ]
elsif node = @nodes[key]
move_to_head(node)
node[3] = value
else
node = [ nil, @head, key, value ]
@head[0] = node
@nodes[key] = @head = node
end
while @nodes.size > @capacity do
@nodes.delete(@tail[2])
@tail = @tail[0]
if @tail
@tail[1] = nil
else
@head = nil
break
end
end
return value
end
def get(key)
node = @nodes[key]
return nil unless node
move_to_head(node)
return node[3]
end
private
def move_to_head(node)
if node == @head
return
elsif node == @tail
@tail = @tail[0]
@tail[1] = nil
end
node[0][1] = node[1]
node[1][0] = node[0] if node[1]
node[0] = nil
node[1] = @head
@head[0] = node
@head = node
end
end
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