## DEV Community

Abhishek Chaudhary

Posted on

# Check If Word Is Valid After Substitutions

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:

• Insert string `"abc"` into any position in `t`. More formally, `t` becomes `tleft + "abc" + tright`, where `t == tleft + tright`. Note that `tleft` and `tright` may be empty.

Return `true` if `s` is a valid string, otherwise, return `false`.

Example 1:

Input: s = "aabcbc"
Output: true
Explanation:
"" -> "abc" -> "aabcbc"
Thus, "aabcbc" is valid.

Example 2:

Input: s = "abcabcababcc"
Output: true
Explanation:
"" -> "abc" -> "abcabc" -> "abcabcabc" -> "abcabcababcc"
Thus, "abcabcababcc" is valid.

Example 3:

Input: s = "abccba"
Output: false
Explanation: It is impossible to get "abccba" using the operation.

Constraints:

• `1 <= s.length <= 2 * 104`
• `s` consists of letters `'a'`, `'b'`, and `'c'`

SOLUTION:

``````class Solution:
def isValid(self, s: str) -> bool:
while "abc" in s:
i = s.index("abc")
s = s[:i] + s[i+3:]
return s == ""
``````