67 lines
1.7 KiB
C++
67 lines
1.7 KiB
C++
// Source : https://leetcode.com/problems/implement-queue-using-stacks/
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// Author : Hao Chen
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// Date : 2015-07-16
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/**********************************************************************************
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*
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* Implement the following operations of a queue using stacks.
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*
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* push(x) -- Push element x to the back of queue.
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*
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* pop() -- Removes the element from in front of queue.
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*
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* peek() -- Get the front element.
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*
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* empty() -- Return whether the queue is empty.
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*
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* Notes:
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*
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* You must use only standard operations of a stack -- which means only push to top,
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* peek/pop from top, size, and is empty operations are valid.
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* Depending on your language, stack may not be supported natively. You may simulate a
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* stack by using a list or deque (double-ended queue), as long as you use only
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* standard operations of a stack.
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* You may assume that all operations are valid (for example, no pop or peek operations
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* will be called on an empty queue).
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*
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**********************************************************************************/
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class Queue {
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public:
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// Push element x to the back of queue.
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void push(int x) {
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s1.push(x);
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}
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// Removes the element from in front of queue.
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void pop(void) {
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transfer(s1, s2);
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s2.pop();
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transfer(s2, s1);
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}
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// Get the front element.
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int peek(void) {
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transfer(s1, s2);
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int ret = s2.top();
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transfer(s2, s1);
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return ret;
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}
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// Return whether the queue is empty.
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bool empty(void) {
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return s1.empty();
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}
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private:
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stack<int> s1, s2;
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void transfer(stack<int>& s1, stack<int>& s2) {
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while(!s1.empty()){
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s2.push(s1.top());
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s1.pop();
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}
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}
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};
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