147 lines
3.6 KiB
Dart
147 lines
3.6 KiB
Dart
/**
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* File: array_deque.dart
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* Created Time: 2023-03-28
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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/* 基于环形数组实现的双向队列 */
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class ArrayDeque {
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late List<int> _nums; // 用于存储双向队列元素的数组
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late int _front; // 队首指针，指向队首元素
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late int _queSize; // 双向队列长度
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/* 构造方法 */
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ArrayDeque(int capacity) {
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this._nums = List.filled(capacity, 0);
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this._front = this._queSize = 0;
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}
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/* 获取双向队列的容量 */
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int capacity() {
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return _nums.length;
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}
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/* 获取双向队列的长度 */
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int size() {
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return _queSize;
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}
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/* 判断双向队列是否为空 */
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bool isEmpty() {
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return _queSize == 0;
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}
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/* 计算环形数组索引 */
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int index(int i) {
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// 通过取余操作实现数组首尾相连
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// 当 i 越过数组尾部后，回到头部
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// 当 i 越过数组头部后，回到尾部
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return (i + capacity()) % capacity();
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}
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/* 队首入队 */
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void pushFirst(int num) {
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if (_queSize == capacity()) {
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throw Exception("双向队列已满");
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}
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// 队首指针向左移动一位
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// 通过取余操作，实现 _front 越过数组头部后回到尾部
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_front = index(_front - 1);
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// 将 num 添加至队首
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_nums[_front] = num;
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_queSize++;
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}
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/* 队尾入队 */
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void pushLast(int num) {
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if (_queSize == capacity()) {
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throw Exception("双向队列已满");
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}
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// 计算尾指针，指向队尾索引 + 1
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int rear = index(_front + _queSize);
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// 将 num 添加至队尾
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_nums[rear] = num;
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_queSize++;
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}
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/* 队首出队 */
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int popFirst() {
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int num = peekFirst();
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// 队首指针向右移动一位
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_front = index(_front + 1);
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_queSize--;
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return num;
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}
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/* 队尾出队 */
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int popLast() {
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int num = peekLast();
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_queSize--;
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return num;
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}
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/* 访问队首元素 */
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int peekFirst() {
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if (isEmpty()) {
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throw Exception("双向队列为空");
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}
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return _nums[_front];
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}
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/* 访问队尾元素 */
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int peekLast() {
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if (isEmpty()) {
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throw Exception("双向队列为空");
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}
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// 计算尾元素索引
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int last = index(_front + _queSize - 1);
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return _nums[last];
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}
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/* 返回数组用于打印 */
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List<int> toArray() {
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// 仅转换有效长度范围内的列表元素
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List<int> res = List.filled(_queSize, 0);
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for (int i = 0, j = _front; i < _queSize; i++, j++) {
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res[i] = _nums[index(j)];
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}
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return res;
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}
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}
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/* Driver Code */
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void main() {
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/* 初始化双向队列 */
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final ArrayDeque deque = ArrayDeque(10);
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deque.pushLast(3);
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deque.pushLast(2);
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deque.pushLast(5);
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print("双向队列 deque = ${deque.toArray()}");
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/* 访问元素 */
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final int peekFirst = deque.peekFirst();
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print("队首元素 peekFirst = $peekFirst");
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final int peekLast = deque.peekLast();
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print("队尾元素 peekLast = $peekLast");
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/* 元素入队 */
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deque.pushLast(4);
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print("元素 4 队尾入队后 deque = ${deque.toArray()}");
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deque.pushFirst(1);
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print("元素 1 队首入队后 deque = ${deque.toArray()}");
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/* 元素出队 */
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final int popLast = deque.popLast();
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print("队尾出队元素 = $popLast，队尾出队后 deque = ${deque.toArray()}");
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final int popFirst = deque.popFirst();
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print("队首出队元素 = $popFirst，队首出队后 deque = ${deque.toArray()}");
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/* 获取双向队列的长度 */
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final int size = deque.size();
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print("双向队列长度 size = $size");
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/* 判断双向队列是否为空 */
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final bool isEmpty = deque.isEmpty();
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print("双向队列是否为空 = $isEmpty");
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}
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