Created
May 1, 2024 20:43
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merge_list.cpp
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| #include <iostream> | |
| #include <string> | |
| using namespace std; | |
| struct Node { | |
| Node *next = nullptr; | |
| int value = 0; | |
| }; | |
| struct List { | |
| Node *head = nullptr, *tail = nullptr; | |
| size_t size = 0; | |
| void print() { | |
| string sep = ""; | |
| for (auto p = head; p; p = p->next) { | |
| cout << sep << p->value; | |
| sep = ", "; | |
| } | |
| cout << " [" << this->size << "]\n"; | |
| } | |
| void emplace_back(int v) { | |
| if (head) { | |
| assert(tail); | |
| tail->next = new Node{}; | |
| tail->next->value = v; | |
| tail = tail->next; | |
| } else { | |
| head = new Node{}; | |
| head->value = v; | |
| tail = head; | |
| } | |
| size++; | |
| } | |
| void split_list(List &left_list, List &right_list) { | |
| assert(size > 1); | |
| // we have had and tail, and size. | |
| Node *p = head; | |
| Node *prev = nullptr; | |
| for (size_t i = 0; i < this->size / 2; ++i) { | |
| prev = p; | |
| p = p->next; | |
| } | |
| cout << "DEBUG: p (middle): " << p->value << "\n"; | |
| cout << "DEBUG: p (prev(middle)): " << prev->value << "\n"; | |
| left_list.head = this->head; | |
| left_list.tail = prev; | |
| left_list.size = this->size / 2; | |
| prev->next = nullptr; | |
| right_list.head = p; | |
| right_list.tail = this->tail; | |
| right_list.size = this->size / 2; | |
| if (this->size % 2 != 0) { | |
| right_list.size++; | |
| } | |
| this->head = nullptr; | |
| this->tail = nullptr; | |
| this->size = 0; | |
| } | |
| void swap(List &l) { | |
| std::swap(l.head, head); | |
| std::swap(l.tail, tail); | |
| std::swap(l.size, size); | |
| } | |
| void sort() { | |
| if (this->size < 2) { | |
| return; | |
| } | |
| List left, right; | |
| split_list(left, right); | |
| left.sort(); | |
| right.sort(); | |
| List merged; | |
| auto take_into_merged = [&merged](Node *p) { | |
| merged.emplace_back(p->value); | |
| }; | |
| Node *p = left.head; | |
| Node *q = right.head; | |
| while (p && q) { | |
| if (p->value < q->value) { | |
| auto t = p->next; | |
| take_into_merged(p); | |
| p = t; | |
| } else { | |
| auto t = q->next; | |
| take_into_merged(q); | |
| q = t; | |
| } | |
| } | |
| for (auto r = p ? p : q; r; r = r->next) { | |
| take_into_merged(r); | |
| } | |
| swap(merged); | |
| } | |
| }; | |
| int main() { | |
| List l; | |
| l.emplace_back(4); | |
| l.emplace_back(5); | |
| l.emplace_back(3); | |
| l.emplace_back(2); | |
| l.emplace_back(1); | |
| l.print(); | |
| l.sort(); | |
| l.print(); | |
| } |
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