Evaluate reverse polish notation

Link: https://leetcode.com/problems/evaluate-reverse-polish-notation/

Solution:

Topics: stack

Intuition
Fun little stack problem! Too easy though. Remember that '-1'.isdigit() returns false, and these numbers can be negative, so either check the counter case or use try/except.

Implementation

def eval_polish(tokens):
	ops = {
		'+': lambda b,a:a+b,   #reverse the paramaters so we can pop twice 
		'-': lambda b,a:a-b,
		'*': lambda b,a:a*b,
		'/': lambda b,a:int(a/b),
	}
	stack = []
	for t in tokens:
		if t in ops:
			stack.append(ops[t](stack.pop(), stack.pop()))
		else:
			stack.append(int(t))
	return stack[-1]
 
#time:
#memory:

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