implement-queue-using-stacks.go

// https://leetcode.com/problems/implement-queue-using-stacks
//  -> [][][][] ->
// <-> [][][][]
// <-> [][][][]

type MyQueue struct {
    front int
    ordered []int
    reversed []int
}


/** Initialize your data structure here. */
func Constructor() MyQueue {
    return MyQueue{
        front: 0,
        ordered: []int{},
        reversed: []int{},
    }
}


/** Push element x to the back of queue. */
func (q *MyQueue) Push(x int)  {
    q.ordered = append(q.ordered, x)
    
    if len(q.ordered) == 1 {
        q.front = x
    }
}


/** Removes the element from in front of queue and returns that element. */
func (q *MyQueue) Pop() int {
    if len(q.reversed) == 0 {
        for _, x := range q.ordered {
            q.reversed = append(q.reversed, x)
        }
        
        q.ordered = q.ordered[:0]
    }
    
    top := q.reversed[0]
    q.reversed = q.reversed[1:]
    
    return top
}


/** Get the front element. */
func (q *MyQueue) Peek() int {
    if len(q.reversed) > 0 {
        return q.reversed[0]
    }
    
    return q.front
}


/** Returns whether the queue is empty. */
func (q *MyQueue) Empty() bool {
    return len(q.ordered) == 0 && len(q.reversed) == 0
}