Task 1. You are given a string containing just numbers and mathematical operator + and *.
You have to read from the string characters, one by one. If it is a digit, then push it in stack.
If it is an operator, pop 2 elements from the stack, apply the operator to those elements, and push the result in stack. If you there is not enough elements in stack, or no operator to apply, return -1.
For example "12+4*7*"
You have to calculate a result like this:
1-> push in stack
2 -> push in stack
+ -> pop 1 from stack, pop 2 from stack, perform 1 + 2 and push 3 in stack
4 -> push in stack
* -> pop 4, pop 3, multiply them and put 12 in stack.
7 -> push in stack
* -> push 7 and 12 from stack and multiply them.
Return 84.
Task 2. It was about dynamic programming/ greedy algorithms.
1 day ticket costs 2 dollars, 7 day ticket costs 7 dollars (valid for sequence of 7 days), one month ticket costs 25.
You are given list of increasing dates you gonna travel.
You have to return minimum possible amount of money you spend on tickets.
For example 1,2,3,4,5,11,12,25
Return 13.