130 lines
3.0 KiB
C++
130 lines
3.0 KiB
C++
#ifndef SJTU_PRIORITY_QUEUE_HPP
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#define SJTU_PRIORITY_QUEUE_HPP
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#include <cstddef>
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#include <functional>
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#include "exceptions.hpp"
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namespace sjtu {
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/**
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* a container like std::priority_queue which is a heap internal.
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* Use Skew heap to implement this priority_queue.
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*/
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template <typename T, class Compare = std::less<T>>
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class priority_queue {
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Compare comp;
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struct Node {
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T value;
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Node *left, *right;
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Node(const T &v) : value(v), left(nullptr), right(nullptr) {}
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} * root;
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size_t node_count;
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void FreeAll(Node *node) {
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if (node == nullptr) return;
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FreeAll(node->left);
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FreeAll(node->right);
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delete node;
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}
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void CopyAll(Node *&dest, Node *src) {
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if (src == nullptr) return;
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dest = new Node(src->value);
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CopyAll(dest->left, src->left);
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CopyAll(dest->right, src->right);
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}
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Node *SkewMerge(Node *a, Node *b) {
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if (a == nullptr) return b;
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if (b == nullptr) return a;
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if (comp(a->value, b->value)) std::swap(a, b);
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a->right = SkewMerge(a->right, b);
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std::swap(a->left, a->right);
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return a;
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}
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public:
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priority_queue() : root(nullptr), node_count(0) {}
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priority_queue(const priority_queue &other) {
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root = nullptr;
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CopyAll(root, other.root);
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node_count = other.node_count;
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}
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/**
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* TODO deconstructor
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*/
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~priority_queue() {
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FreeAll(root);
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root = nullptr;
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}
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/**
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* TODO Assignment operator
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*/
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priority_queue &operator=(const priority_queue &other) {
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if (this == &other) return *this;
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FreeAll(root);
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root = nullptr;
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CopyAll(root, other.root);
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node_count = other.node_count;
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return *this;
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}
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/**
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* get the top of the queue.
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* @return a reference of the top element.
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* throw container_is_empty if empty() returns true;
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*/
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const T &top() const {
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if (empty()) throw container_is_empty();
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return root->value;
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}
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/**
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* TODO
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* push new element to the priority queue.
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*/
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void push(const T &e) {
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Node *new_node = new Node(e);
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try {
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root = SkewMerge(root, new_node);
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} catch (...) {
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delete new_node;
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throw;
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}
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++node_count;
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}
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/**
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* TODO
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* delete the top element.
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* throw container_is_empty if empty() returns true;
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*/
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void pop() {
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if (empty()) throw container_is_empty();
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Node *old_root = root;
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root = SkewMerge(root->left, root->right);
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delete old_root;
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--node_count;
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}
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/**
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* return the number of the elements.
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*/
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size_t size() const { return node_count; }
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/**
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* check if the container has at least an element.
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* @return true if it is empty, false if it has at least an element.
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*/
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bool empty() const { return node_count == 0; }
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/**
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* merge two priority_queues with at most O(logn) complexity.
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* clear the other priority_queue.
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*/
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void merge(priority_queue &other) {
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if (other.root == root) return;
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root = SkewMerge(root, other.root);
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node_count += other.node_count;
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other.root = nullptr;
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other.node_count = 0;
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}
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};
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} // namespace sjtu
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#endif
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