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‎ImplementStackUsingQueues/implement_stack_using_queues.dart

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/*
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-* Implement Stack using Queues *-
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Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).
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Implement the MyStack class:
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void push(int x) Pushes element x to the top of the stack.
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int pop() Removes the element on the top of the stack and returns it.
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int top() Returns the element on the top of the stack.
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boolean empty() Returns true if the stack is empty, false otherwise.
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Notes:
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You must use only standard operations of a queue, which means that only push to back, peek/pop from front, size and is empty operations are valid.
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Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations.
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Example 1:
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Input
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["MyStack", "push", "push", "top", "pop", "empty"]
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[[], [1], [2], [], [], []]
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Output
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[null, null, null, 2, 2, false]
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Explanation
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MyStack myStack = new MyStack();
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myStack.push(1);
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myStack.push(2);
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myStack.top(); // return 2
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myStack.pop(); // return 2
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myStack.empty(); // return False
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Constraints:
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1 <= x <= 9
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At most 100 calls will be made to push, pop, top, and empty.
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All the calls to pop and top are valid.
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Follow-up: Can you implement the stack using only one queue?
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*/
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import 'dart:collection';
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// Runtime: 469 ms, faster than 50.00% of Dart online submissions for Implement Stack using Queues.
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// Memory Usage: 143 MB, less than 50.00% of Dart online submissions for Implement Stack using Queues.
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class MyStack {
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Queue<int> queueOne = Queue();
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Queue<int> queueTwo = Queue();
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MyStack() {
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this.queueOne;
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this.queueTwo;
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}
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void push(int x) {
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if (queueOne.isEmpty && queueTwo.isEmpty) {
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queueOne.add(x);
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} else if (queueOne.isEmpty) {
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queueOne.add(x);
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while (queueTwo.isNotEmpty) {
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queueOne.add(queueTwo.removeFirst());
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}
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} else if (queueTwo.isEmpty) {
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queueTwo.add(x);
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while (queueOne.isNotEmpty) {
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queueTwo.add(queueOne.removeFirst());
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}
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}
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}
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int pop() {
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if (queueOne.isNotEmpty) {
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return queueOne.removeFirst();
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} else if (queueTwo.isNotEmpty)
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return queueTwo.removeFirst();
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else
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return -1;
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}
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int top() {
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if (queueOne.isNotEmpty) {
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return queueOne.first;
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} else if (queueTwo.isNotEmpty)
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return queueTwo.first;
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else
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return -1;
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}
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bool empty() {
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return queueTwo.isEmpty && queueOne.isEmpty;
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}
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}
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/*
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class MyStack {
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MyStack() {
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}
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void push(int x) {
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}
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int pop() {
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}
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int top() {
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}
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bool empty() {
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}
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}
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*/
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class MyStacking {
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// Runtime: 467 ms, faster than 50.00% of Dart online submissions for Implement Stack using Queues.
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// Memory Usage: 143 MB, less than 75.00% of Dart online submissions for Implement Stack using Queues.
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Queue<int> queue = Queue();
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MyStacking() {
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this.queue;
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}
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void push(int x) {
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queue.add(x);
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for (int i = 0; i < queue.length - 1; i++) {
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queue.add(queue.removeFirst());
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}
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}
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int pop() {
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return queue.removeFirst();
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}
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int top() {
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return queue.first;
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}
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bool empty() {
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return queue.isEmpty;
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}
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}

‎ImplementStackUsingQueues/implement_stack_using_queues.go

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package main
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// Runtime: 0 ms, faster than 100.00% of Go online submissions for Implement Stack using Queues.
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// Memory Usage: 1.9 MB, less than 82.31% of Go online submissions for Implement Stack using Queues.
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type MyStack struct {
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queue []int
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}
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/** Initialize your data structure here. */
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func Constructor() MyStack {
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return MyStack{[]int{}}
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}
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/** Push element x onto stack. */
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func (this *MyStack) Push(x int) {
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this.queue = append(this.queue[:0], append([]int{x}, this.queue[0:]...)...) // prepend
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}
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/** Removes the element on top of the stack and returns that element. */
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func (this *MyStack) Pop() int {
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temp := this.queue[0]
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this.queue = this.queue[1:]
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return temp
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}
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/** Get the top element. */
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func (this *MyStack) Top() int {
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return this.queue[0]
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}
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/** Returns whether the stack is empty. */
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func (this *MyStack) Empty() bool {
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return len(this.queue) == 0
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}

‎ImplementStackUsingQueues/implement_stack_using_queues.md

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# 🔥 Implement Stack using Queues 🔥 || 3 Solutions || Simple Fast and Easy || with Explanation
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## Solution - 1 Single Queue
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```dart
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import 'dart:collection';
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class MyStack {
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// Runtime: 467 ms, faster than 50.00% of Dart online submissions for Implement Stack using Queues.
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// Memory Usage: 143 MB, less than 75.00% of Dart online submissions for Implement Stack using Queues.
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Queue<int> queue = Queue();
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MyStack() {
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this.queue;
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}
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void push(int x) {
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queue.add(x);
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for (int i = 0; i < queue.length - 1; i++) {
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queue.add(queue.removeFirst());
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}
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}
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int pop() {
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return queue.removeFirst();
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}
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int top() {
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return queue.first;
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}
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bool empty() {
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return queue.isEmpty;
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}
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}
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```
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## Solution - 2 Double Queue
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```dart
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import 'dart:collection';
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class MyStack {
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// Runtime: 469 ms, faster than 50.00% of Dart online submissions for Implement Stack using Queues.
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// Memory Usage: 143 MB, less than 50.00% of Dart online submissions for Implement Stack using Queues.
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Queue<int> queueOne = Queue();
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Queue<int> queueTwo = Queue();
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MyStack() {
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this.queueOne;
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this.queueTwo;
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}
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void push(int x) {
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if (queueOne.isEmpty && queueTwo.isEmpty) {
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queueOne.add(x);
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} else if (queueOne.isEmpty) {
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queueOne.add(x);
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while (queueTwo.isNotEmpty) {
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queueOne.add(queueTwo.removeFirst());
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}
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} else if (queueTwo.isEmpty) {
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queueTwo.add(x);
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while (queueOne.isNotEmpty) {
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queueTwo.add(queueOne.removeFirst());
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}
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}
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}
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int pop() {
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if (queueOne.isNotEmpty) {
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return queueOne.removeFirst();
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} else if (queueTwo.isNotEmpty)
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return queueTwo.removeFirst();
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else
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return -1;
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}
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int top() {
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if (queueOne.isNotEmpty) {
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return queueOne.first;
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} else if (queueTwo.isNotEmpty)
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return queueTwo.first;
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else
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return -1;
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}
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bool empty() {
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return queueTwo.isEmpty && queueOne.isEmpty;
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}
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}
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```
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## Bonus Solution - Go 😈
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```go
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type MyStack struct {
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queue []int
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}
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/** Initialize your data structure here. */
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func Constructor() MyStack {
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return MyStack{ []int{} }
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}
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/** Push element x onto stack. */
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func (this *MyStack) Push(x int) {
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this.queue = append(this.queue[:0], append([]int{x}, this.queue[0:]...)...) // prepend
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}
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/** Removes the element on top of the stack and returns that element. */
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func (this *MyStack) Pop() int {
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temp := this.queue[0]
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this.queue = this.queue[1:]
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return temp
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}
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/** Get the top element. */
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func (this *MyStack) Top() int {
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return this.queue[0]
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}
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/** Returns whether the stack is empty. */
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func (this *MyStack) Empty() bool {
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return len(this.queue) == 0
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}
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```

‎README.md

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- [Reverse Linked List](ReverseLinkedList/reverse_linked_list.dart)
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- [Contains Duplicate](ContainsDuplicate/contains_duplicate.dart)
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- [Contains Duplicate II](ContainsDuplicate-II/contains_duplicate_II.dart)
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- [Implement Stack using Queues](ImplementStackUsingQueues/implement_stack_using_queues.dart)
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## Reach me via
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