#!/usr/bin/env python3
# Author: Dr. Robert Heckendorn, Computer Science Department, University of Idaho, 2013
from copy import *


## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 
#
# LINK A DIGRAPH AS A GRAPH by adding backedges for every
# directed edge.
def relink(g) :
    for i in range(0, len(g)) :
        for j in g[i] :
            if i!=j : g[j].add(i)   # prevent the add from changing g[i]
    return g                  # note that g was changed and really doesn't have to be returned




## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 
#
# SIMPLE ARRAY
#

# simple utility 1D array function
def array(size, value) : 
    a = []
    for i in range(0, size) : 
        a.append(deepcopy(value))
    return a


## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 
#
# STACK AND QUEUE
#
# This provides very simple stack and queue operations

# LEFT SIDE
def pushLeft(l, item) :
    l.insert(0, item)

def popLeft(l) :
    if len(l)==0 :
        print("ERROR(popLeft): no elements in list")
        return None
    tmp = l[0]
    del l[0]
    return tmp

def topLeft(l) :
    if len(l)==0 :
        print("ERROR(topLeft): no elements in list")
        return None
    return l[0]

# RIGHT SIDE
def pushRight(l, item) :
    l.append(item)

def popRight(l) :
    if len(l)==0 :
        print("ERROR(popRight): no elements in list")
        return None
    return l.pop()

def topRight(l) :
    if len(l)==0 :
        print("ERROR(topRight): no elements in list")
        return None
    return l[-1]

# z = ["ant", "bat", "cow"]
# print(z)
# print("R:", topRight(z))
# print("L:", topLeft(z))
# pushLeft(z, "aardvark")
# pushRight(z, "dog")
# print(z)
# print(popLeft(z))
# print(z)
# print(popRight(z))
# print(z)
# print(popLeft(z))
# print(z)
# print(popRight(z))
# print(z)
# print(popLeft(z))
# print(z)
# print(popRight(z))
# print(z)
# print("R:", topRight(z))
# print("L:", topLeft(z))