grid47 Exploring patterns and algorithms
Aug 31, 2024
5 min read
Solution to LeetCode 678: Valid Parenthesis String Problem
Given a string consisting of ‘(’, ‘)’, and ‘’, determine if the string is valid according to the following rules. ‘’ can be treated as a left parenthesis, a right parenthesis, or an empty string.
Problem
Approach
Steps
Complexity
Input: The input is a string containing only '(', ')', and '*' characters.
Example: "(*)"
Constraints:
• 1 <= s.length <= 100
• s[i] is either '(', ')', or '*'
Output: The output should be true if the string is valid, otherwise false.
Example: true
Constraints:
• The output will be a boolean value, either true or false.
Goal: Efficiently validate the string using a stack to account for both parentheses and '*' characters.
Steps:
• 1. Traverse the string character by character.
• 2. Use two stacks: one for tracking '(' characters and one for tracking '*' characters.
• 3. If a ')' is encountered, check if there is a matching '(' or '*' to balance it.
• 4. After traversal, check if all '(' have corresponding ')' or '*' to balance them.
Goal: The constraints ensure that the problem remains manageable within time and space limits.
Steps:
• The length of the string s is between 1 and 100.
• The string contains only the characters '(', ')', and '*'.
Assumptions:
• All parentheses are balanced by either another parenthesis or a '*' character.
• Input: "(*)"
• Explanation: In this example, '*' can be treated as either a '(' or a ')', making the string valid.
• Input: "(*))"
• Explanation: The string is valid because '*' can be treated as '(', and the remaining parentheses are balanced.
Approach: We can use two stacks to track the positions of parentheses and '*' characters, ensuring the string remains valid.
Observations:
• We need to ensure that the parentheses are properly balanced, with '*' acting as a wildcard.
• Using two stacks will allow us to handle matching of both '(' and ')' while also utilizing '*' as a flexible placeholder.
Steps:
• 1. Iterate through the string to check for '(' and ')'.
• 2. Track positions of '(' and '*' using stacks.
• 3. For each ')', attempt to match it with a '(' from the stack. If none is available, use '*' if possible.
• 4. After the loop, check if there are any unmatched '(' characters left.
Empty Inputs:
• An empty string is considered valid.
Large Inputs:
• The string length can be up to 100, which is manageable within the time constraints.
Special Values:
• A string consisting only of '*' characters is valid because '*' can be treated as empty, '(' or ')'.
Constraints:
• Ensure efficient handling of edge cases with '*' characters.
