Merge pull request #1129 from mahek0620/queue-using-stack

Added lc solution 232

Author: ajay-dhangar

dsa-solutions/lc-solutions/0200-0299/0232-Implement-Queue-using-Stack.md

@@ -0,0 +1,227 @@
+---
+id: queue-using-stacks
+title: Implement Queue using Stacks
+sidebar_label: Implement Queue using Stacks
+tags:
+- Data Structures
+- Stack
+- Queue
+- Python
+- Java
+- C++
+description: "This document provides an implementation of a queue using stacks, supporting push, pop, peek, and empty operations."
+---
+
+### Examples
+
+**Example 1:**
+
+```
+
+Input
+["MyQueue", "push", "push", "peek", "pop", "empty"]
+[[], [1], [2], [], [], []]
+Output
+[null, null, null, 1, 1, false]
+
+Explanation
+MyQueue myQueue = new MyQueue();
+myQueue.push(1); // queue is: [1]
+myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)
+myQueue.peek(); // return 1
+myQueue.pop(); // return 1, queue is [2]
+myQueue.empty(); // return false
+```
+
+### Constraints
+
+- $1 <= x <= 9$
+- At most 100 calls will be made to push, pop, peek, and empty.
+- All the calls to pop and peek are valid.
+
+## Problem Statement
+Implement a first-in-first-out (FIFO) queue using two stacks. The implemented queue should support the following operations:
+- `push(x)`: Pushes element `x` to the back of the queue.
+- `pop()`: Removes the element from the front of the queue and returns it.
+- `peek()`: Returns the element at the front of the queue without removing it.
+- `empty()`: Returns whether the queue is empty.
+
+## Approach
+To achieve FIFO order using stacks, we can use two stacks:
+- `stack1`: Used for enqueue operations (`push`).
+- `stack2`: Used for dequeue operations (`pop` and `peek`).
+
+### Operations Details:
+1. **Push Operation (`push(x)`)**:
+   - Simply push the element onto `stack1`.
+
+2. **Pop Operation (`pop()`)**:
+   - If `stack2` is empty, transfer all elements from `stack1` to `stack2`. Then, pop the top element from `stack2`.
+
+3. **Peek Operation (`peek()`)**:
+   - If `stack2` is empty, transfer all elements from `stack1` to `stack2`. Then, peek at the top element of `stack2`.
+
+4. **Empty Check (`empty()`)**:
+   - The queue is considered empty if both `stack1` and `stack2` are empty.
+
+#### Code in Different Languages
+
+<Tabs>
+  <TabItem value="Python" label="Python" default>
+  <SolutionAuthor name="@mahek0620"/>
+   ```python
+
+    class MyQueue:
+
+    def __init__(self):
+        self.stack1 = []  # Stack for enqueue operations
+        self.stack2 = []  # Stack for dequeue operations
+
+    def push(self, x):
+        """
+        Push element x to the back of the queue.
+        """
+        self.stack1.append(x)
+
+    def pop(self):
+        """
+        Removes the element from the front of the queue and returns it.
+        """
+        self.move_elements()
+        return self.stack2.pop()
+
+    def peek(self):
+        """
+        Returns the element at the front of the queue without removing it.
+        """
+        self.move_elements()
+        return self.stack2[-1]
+
+    def empty(self):
+        """
+        Returns whether the queue is empty.
+        """
+        return len(self.stack1) == 0 and len(self.stack2) == 0
+
+    def move_elements(self):
+        """
+        Moves elements from stack1 to stack2 if stack2 is empty.
+        """
+        if not self.stack2:
+            while self.stack1:
+                self.stack2.append(self.stack1.pop())
+
+    ```
+  </TabItem>
+  <TabItem value="Java" label="Java">
+  <SolutionAuthor name="@mahek0620"/>
+   ```java
+    
+    import java.util.Stack;
+
+    class MyQueue {
+    private Stack<Integer> stack1;
+    private Stack<Integer> stack2;
+
+    /** Initialize your data structure here. */
+    public MyQueue() {
+        stack1 = new Stack<>();
+        stack2 = new Stack<>();
+    }
+    
+    /** Push element x to the back of queue. */
+    public void push(int x) {
+        stack1.push(x);
+    }
+    
+    /** Removes the element from in front of queue and returns that element. */
+    public int pop() {
+        moveElements();
+        return stack2.pop();
+    }
+    
+    /** Get the front element. */
+    public int peek() {
+        moveElements();
+        return stack2.peek();
+    }
+    
+    /** Returns whether the queue is empty. */
+    public boolean empty() {
+        return stack1.isEmpty() && stack2.isEmpty();
+    }
+    
+    private void moveElements() {
+        if (stack2.isEmpty()) {
+            while (!stack1.isEmpty()) {
+                stack2.push(stack1.pop());
+            }
+        }
+    }
+    }
+
+    ```
+  </TabItem>
+  <TabItem value="C++" label="C++">
+  <SolutionAuthor name="@mahek0620"/>
+   ```cpp
+   
+    #include <stack>
+
+    class MyQueue {
+    private:
+    std::stack<int> stack1;
+    std::stack<int> stack2;
+    
+    public:
+    /** Initialize your data structure here. */
+    MyQueue() {
+        
+    }
+    
+    /** Push element x to the back of queue. */
+    void push(int x) {
+        stack1.push(x);
+    }
+    
+    /** Removes the element from in front of queue and returns that element. */
+    int pop() {
+        moveElements();
+        int front = stack2.top();
+        stack2.pop();
+        return front;
+    }
+    
+    /** Get the front element. */
+    int peek() {
+        moveElements();
+        return stack2.top();
+    }
+    
+    /** Returns whether the queue is empty. */
+    bool empty() {
+        return stack1.empty() && stack2.empty();
+    }
+    
+    private:
+    void moveElements() {
+        if (stack2.empty()) {
+            while (!stack1.empty()) {
+                stack2.push(stack1.top());
+                stack1.pop();
+            }
+        }
+    }
+    };
+
+    ```
+
+  </TabItem>
+</Tabs>
+
+
+## References
+
+- **LeetCode Problem:** [LeetCode Problem](https://leetcode.com/problems/implement-queue-using-stacks/)
+- **Solution Link:** [Implement-Queue-Using-Stacks Solution on LeetCode](https://leetcode.com/problems/implement-queue-using-stacks/solutions/)
+- **Authors GeeksforGeeks Profile:** [Mahek Patel](https://leetcode.com/u/mahekrpatel611/)