well..wasting memory space???dude space/memory is what you pay for time...if you want your code to give quick and efficient response you use memory rather than cpu computation..also i totally agree i completely miss the stack concept...this is because i want my code to be most efficient and fast..using stack operations like push and pop takes time and cpu (trust me i've sumitted codes using stack that were accurate but it resulted it timeout )...if you're a python programmer timeit my code against yours..i can bet my code will give you quick and efficient result than yours....good day.