Description:
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).
Solution:
class Queue {
private:
stack<int> input;
stack<int> output;
public:
// Push element x to the back of queue.
void push(int x) {
input.push(x);
}
// Removes the element from in front of queue.
void pop(void) {
peek();
output.pop();
}
// Get the front element.
int peek(void) {
if (output.empty()) {
while (!input.empty()) {
output.push(input.top());
input.pop();
}
}
return output.top();
}
// Return whether the queue is empty.
bool empty(void) {
return input.empty() && output.empty();
}
};
转载于:https://www.cnblogs.com/deofly/p/implement-queue-using-stacks.html
