30:00
Given a string s containing only three types of characters: '(', ')' and '*', return true if s is valid.
1≤s.length≤1001 \leq s.\text{length} \leq 1001≤s.length≤100
s[i] is '(', ')', or '*'.
s[i]
'('
')'
'*'
Start: low=0, high=0
(
*
)