We are given that the string "abc" is valid.
From any valid string V, we may split V into two pieces X
and Y such that X + Y (X concatenated with
Y) is equal to V. (X or Y may be
empty.) Then, X + "abc" + Y is also valid.
If for example S = "abc", then examples of valid strings are: "abc",
"aabcbc", "abcabc", "abcabcababcc". Examples of
invalid strings are: "abccba", "ab",
"cababc", "bac".
Return true if and only if the given string S is valid.
Example 1:
Input: "aabcbc" Output: true Explanation: We start with the valid string "abc". Then we can insert another "abc" between "a" and "bc", resulting in "a" + "abc" + "bc" which is "aabcbc".
Example 2:
Input: "abcabcababcc" Output: true Explanation: "abcabcabc" is valid after consecutive insertings of "abc". Then we can insert "abc" before the last letter, resulting in "abcabcab" + "abc" + "c" which is "abcabcababcc".
Example 3:
Input: "abccba" Output: false
Example 4:
Input: "cababc" Output: false