Question：
Given an array and a value, remove all instances of that value in place and return the new length.
Do not allocate extra space for another array, you must do this in place with constant memory.
The order of elements can be changed. It doesn't matter what you leave beyond the new length.
Example:
Given input arraynums=[3,2,2,3],val=3
Your function should return length = 2, with the first two elements of nums being 2.
Answer :
note:
-1- Pay attention to the requirement, we have to use the same array to accomplish this question.
-2- The function slice is helpful, necessary to memorize it and the also those related.
Plus: another method~
