Update stack.py
Update stack.py
mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview