README.md

225. Implement Stack using Queues

Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

Example:

MyStack stack = new MyStack(); stack.push(1); stack.push(2); stack.top(); // returns 2 stack.pop(); // returns 2 stack.empty(); // returns false 

Note:

• You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
• You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

Solutions (Rust)

1. One Queue

structMyStack{queue:Vec<i32>,}/** * `&self` means the method takes an immutable reference. * If you need a mutable reference, change it to `&mut self` instead. */implMyStack{/** Initialize your data structure here. */fnnew() -> Self{Self{queue:Vec::new(),}}/** Push element x onto stack. */fnpush(&mutself,x:i32){self.queue.push(x);for _ in1..self.queue.len(){let temp = self.queue.remove(0);self.queue.push(temp)}}/** Removes the element on top of the stack and returns that element. */fnpop(&mutself) -> i32{self.queue.remove(0)}/** Get the top element. */fntop(&self) -> i32{*self.queue.first().unwrap()}/** Returns whether the stack is empty. */fnempty(&self) -> bool{self.queue.is_empty()}}/** * Your MyStack object will be instantiated and called as such: * let obj = MyStack::new(); * obj.push(x); * let ret_2: i32 = obj.pop(); * let ret_3: i32 = obj.top(); * let ret_4: bool = obj.empty(); */