Check If Word Is Valid After Substitutions - Problem
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 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.
Input & Output
Example 1 — Valid String
$
Input:
s = "aabcbc"
›
Output:
true
💡 Note:
Start with empty string, insert "abc" to get "abc", then insert "abc" at beginning to get "abcabc", but wait - we can think of it as: "aabcbc" → remove "abc" from middle → "abc" → remove "abc" → empty string.
Example 2 — Invalid String
$
Input:
s = "abacbc"
›
Output:
false
💡 Note:
Cannot form this by inserting only "abc" patterns. The 'a' in the middle breaks the pattern.
Example 3 — Simple Valid
$
Input:
s = "abcabcabc"
›
Output:
true
💡 Note:
Three "abc" patterns in sequence can be built by inserting "abc" three times.
Constraints
- 1 ≤ s.length ≤ 2 × 104
- s consists only of letters 'a', 'b', and 'c'
Visualization
Tap to expand
Understanding the Visualization
1
Input
String containing only a, b, c characters
2
Process
Remove abc patterns using stack or string replacement
3
Output
True if string reduces to empty, false otherwise
Key Takeaway
🎯 Key Insight: Valid strings can always be reduced to empty by removing "abc" patterns
💡
Explanation
AI Ready
💡 Suggestion
Tab
to accept
Esc
to dismiss
// Output will appear here after running code