public class Solution
extends Object
1003 - Check If Word Is Valid After Substitutions\.
Medium
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'`