LeetCode 之 Implement Queue using Stacks — C++ 實現
阿新 • • 發佈：2019-02-10
Implement Queue using Stacks
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.
- You must use only standard operations of a stack -- which means only
push to top,peek/pop from top,size, andis emptyoperations 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).
- push(x) -- 將元素放入隊尾。
- pop() -- 移除佇列頭的元素。
- peek() -- 返回佇列頭元素。
- empty() -- 返回佇列是否為空。
- 只能使用棧的標準操作--即
push to top，peek/pop from top，size，和 is empty 合法。 - 使用的語言不一定有棧結構，但可以使用連結串列或佇列模擬棧，只要使用棧的標準操作就可以。
- 假設所有操作都合法（例如，當佇列空時不會執行 pop 和 peek 操作）。
因為棧是 FILO 結構，佇列是 LIFO 結構，入隊操作和壓棧操作一樣，但是出棧操作和出隊操作相反，可以使用輔助棧，出隊時將資料壓入輔助棧，返回棧底（隊頭）元素後再將元素存回原來的棧。
class Queue {
public:
// Push element x to the back of queue.
void push(int x) {
squeue.push(x);
}
// Removes the element from in front of queue.
void pop(void) {
stack<int> temp;
stackSwap(squeue, temp);
temp.pop();
stackSwap(temp, squeue);
return;
}
// Get the front element.
int peek(void) {
int ret = 0;
stack<int> temp;
stackSwap(squeue, temp);
ret = temp.top();
stackSwap(temp, squeue);
return ret;
}
// Return whether the queue is empty.
bool empty(void) {
return squeue.empty();
}
void stackSwap(stack<int> &src, stack<int> &dst)
{
int srcSize = src.size();
for(int i = 0; i < srcSize; ++i)
{
dst.push(src.top());
src.pop();
}
return;
}
private:
stack<int> squeue;
};