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Implement Queue using Stacks
Total Accepted: 93 Total Submissions: 256Implement 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.
- You must use only standard operations of a stack -- which means only
push to top
,peek/pop from top
,size
, andis 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).
[思路]
用两个stacks实现一个queue.
[CODE]
class MyQueue {
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();
}
}
本文标签: LeetCodeimplementStacksQueue
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