A non-empty array a of length n is called an array of all possibilities if it contains all numbers between [0,a.length-1].Write a method named isAllPossibilities that accepts an integer array and returns true
if the array is an array of all possibilities, else false.
Example:
a=[1,2,0,3]
a.length-1=3
a includes [0,3] ,hence the function should return true