Check If Word Is Valid After Substitutions

Input: s = "aabcbc"

Output: true

"" -> "abc" -> "aabcbc". We can insert "abc" at position 1 (after the first "a"), producing the valid string.

Input: s = "abcabcababcc"

Output: true

"" -> "abc" -> "abcabc" -> "abcabcabc" -> "abcabcababcc". Multiple insertions at different positions produce this valid string.

Input: s = "abccba"

Output: false

It is impossible to produce "abccba" using only insertions of "abc". The sequence "cba" cannot be formed by any valid insertion.

Problem