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advent of code 2021

day 10

syntax scoring

pythonadvent of code 2021stack

using a stack, you can figure out exactly where does the string become invalid, if at all

python
m = {"{":"}", "(":")", "[":"]", "<":">"}
def parse(l):
    s = []
    for c in l:
        if c in m:
            s.append(c)    
        elif s and m[s[-1]] == c:
            s.pop()
        else:
            return s, c
    return s, None

if the stack is not empty at the end, it means it is incomplete and that the only way to complete it would be to reverse the stack and append it to the original string

python
mm = {"(":1, "[":2, "{":3, "<":4}
def encode(s):
    rr = 0
    # reversed because it is a stack
    for c in reversed(s):
        rr *= 5
        rr += mm[c]
    return rr