Valid Parenthesis String Problem
Description
LeetCode Problem 678.
Given a string s containing only three types of characters: ‘(‘, ‘)’ and ‘*’, return true if s is valid.
The following rules define a valid string:
- Any left parenthesis ‘(‘ must have a corresponding right parenthesis ‘)’.
- Any right parenthesis ‘)’ must have a corresponding left parenthesis ‘(‘.
- Left parenthesis ‘(‘ must go before the corresponding right parenthesis ‘)’.
- ’*’ could be treated as a single right parenthesis ‘)’ or a single left parenthesis ‘(‘ or an empty string “”.
Example 1:
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Input: s = "()"
Output: true
Example 2:
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Input: s = "(*)"
Output: true
Example 3:
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Input: s = "(*))"
Output: true
Constraints:
- 1 <= s.length <= 100
- s[i] is ‘(‘, ‘)’ or ‘*’.
Sample C++ Code
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class Solution {
public:
bool checkValidString(string s) {
int lower = 0, upper = 0;
for (char c : s) {
if (c == '(') {
lower ++;
upper ++;
} else if (c == ')') {
lower --;
upper --;
} else {
// * encountered
lower --;
upper ++;
}
lower = max(lower, 0);
if (upper < 0)
// unmatched ')' found in the middle of string
return false;
}
return lower == 0;
}
};