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You've got an inefficiency in your code, as you always do replacements 3/2 times the length of the string. That is unnecessarily expensive. By instead testing in each iteration whether the length ...
Answer
#1: Initial revision
by
celtschk
·
2021-09-20T07:45:03Z (over 3 years ago)
You've got an inefficiency in your code, as you always do replacements 3/2 times the length of the string. That is unnecessarily expensive.
By instead testing in each iteration whether the length actually changed, you get a much improved performance:
```
def is_valid(s: str) -> bool:
if len(s) % 1 != 0:
return False
# this initial value causes the loop to be skipped entirely for empty strings
prevlen = 0
# stop as soon as no further replacements have been made
while len(s) != prevlen:
prevlen = len(s)
s = s.replace("()", "").replace("[]", "").replace("{}", "")
return len(s) == 0
```
I've put it together with your code and hkotsubo's timing code on tio.run, and got the following:
```
--------------
Unbalanced in the middle
0.04957069695228711
0.002779866976197809
--------------
Unbalanced in the beginning
0.05233071401016787
0.0026999289984814823
--------------
Unbalanced in the end
0.05092682002577931
0.0026755660073831677
--------------
Balanced
0.047405752004124224
0.002398615994025022
```
[Try it online!](https://tio.run/##vVTLjtowFN3nK05BlW3KdBi6Q6KLLvoH7YaiypAbsOrYke2kQohvpzePKRraUVnM9G7i3Oc59zipDmnv3YfzeQwfzM44bdFQiMa7LKcCJn7V1uQyLhBTULj7iI33dpGBzRSw5GRUeIs53iwx6/2tBUp1cPisbaSs8xY@wMA4BO12JIfK@3vM1aUsYon4PlBl9ZbkSKrRFKORunhW62vP8dR7@inD3KH7kjFl2RimrIJvKL/i9r25jdzDP8mNkfYmMjuTTLtCbWvCVteRIkcI1vsKyWNDiD9MVTEUcskEsoduMVRW6dCiMG4Xu45VoIYBoGPQj4iJm@iI6L1rn86jqAO3Dxi2UXLTiL1uiCdxcalz6op/7o2lR0JMZuh@oXQZ1ye9qiLnIvgSyZRkUquND2l4a8UKtcPDrHNEkN7ukSimrNJBly2aI4Sryw0FgQUnTiF21m9YC7HAcJIKpyxrk8VxJaVS66NUK6nWp5PAhItmM46@47BSYjg9m1ixKEmKuyf2zX1xPEm7LUvJl7oVuTR5bkmooaJnJMXvb0iJKSaTnof6M@vxNl6l9TRuwPlSNDbE/wHHF/F1mPwN4PypIDdDJZf/Z5DPQPs0AHthNOdf "Python 3 – Try It Online")