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                合規國際互聯網加速 OSASE為企業客戶提供高速穩定SD-WAN國際加速解決方案。 廣告
                Implement the following operations of a queue using stacks. push(x) – Push element x to the back of queue. pop() – Removes the element from in front of queue. peek() – Get the front element. empty() – Return whether the queue is empty. Notes: You must use only standard operations of a stack – which means only push to top, peek/pop from top, size, and is empty operations are valid. Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack. You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue). ~~~ class MyQueue { //Stack<Integer> stack1=new Stack(); //Stack<Integer> stack2=new Stack(); Stack<Integer> s1 = new Stack<>(); Stack<Integer> s2 = new Stack<>(); // Push element x to the back of queue. public void push(int x) { s1.push(x); } // Removes the element from in front of queue. public void pop() { if(!s2.isEmpty()) s2.pop(); else { while(!s1.isEmpty()) s2.push(s1.pop()); s2.pop(); } } // Get the front element. public int peek() { if(!s2.isEmpty()) return s2.peek(); else { while(!s1.isEmpty()) s2.push(s1.pop()); return s2.peek(); } } // Return whether the queue is empty. public boolean empty() { return s1.empty() && s2.empty(); } } ~~~
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