Given a string s, determine if it is valid.
A string s is valid if, starting with an empty string t = "", you can transform t into s after performing the following operation any number of times:
"abc" into any position in t. More formally, t becomes t_left + "abc" + t_right, where t == t_left + t_right. Note that t_left and t_right may be empty.Return true if s is a valid string, otherwise, return false.
1 <= s.length <= 2 * 10^4s consists of letters 'a', 'b', and 'c' onlys = "aabcbc"trues = "abcabcababcc"trues = "abccba"false