126 lines
2.7 KiB
C++
126 lines
2.7 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2019 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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#include "../debug/assert.hpp"
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#include <iterator>
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#include <utility>
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namespace cruft::list {
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template <typename ValueT>
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struct node {
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node *next;
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ValueT data;
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bool operator< (node const &rhs) const
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{
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return data < rhs.data;
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}
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};
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template <typename ValueT>
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node<ValueT>*
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midpoint (node<ValueT> *first, node<ValueT> *last)
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{
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auto slow = first;
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auto fast = first->next;
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while (fast != last->next) {
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fast = fast->next;
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if (fast == last->next)
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return slow;
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fast = fast->next;
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slow = slow->next;
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}
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return slow;
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}
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template <typename ValueT>
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node<ValueT>*
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merge (
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node<ValueT> *first,
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node<ValueT> *middle,
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node<ValueT> *last
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) {
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CHECK (first);
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CHECK (middle);
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CHECK (last);
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if (first == last)
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return first;
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auto extract = [&] () {
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auto &target = *first < *middle ? first : middle;
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auto res = target;
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target = target->next;
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return res;
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};
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node<ValueT> *cursor = extract ();
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auto head = cursor;
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while (first && middle && first != middle && middle != last->next) {
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auto target = extract ();
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cursor->next = target;
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cursor = target;
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}
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if (first == middle || !first)
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cursor->next = middle;
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else if (middle == last->next || !middle)
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cursor->next = first;
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return head;
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}
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// Merge sort for singly-linked lists
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template <typename ValueT>
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node<ValueT>*
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sort (node<ValueT> *first, node<ValueT> *last)
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{
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if (first == last)
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return first;
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auto a_end = ::cruft::list::midpoint (first, last);
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auto middle = a_end->next;
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a_end->next = nullptr;
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auto a = ::cruft::list::sort (first, a_end);
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auto b = ::cruft::list::sort (middle, last);
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return ::cruft::list::merge (a, b, last);
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}
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template <typename ValueT>
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bool is_sorted (node<ValueT> const *head)
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{
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if (!head->next)
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return true;
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auto a = head;
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auto b = head->next;
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while (b) {
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if (*b < *a)
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return false;
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a = a->next;
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b = b->next;
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}
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return true;
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}
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}
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