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Given a string s of '(' , ')' and lowercase English characters.
Your task is to remove the minimum number of parentheses ( '(' or ')', in any positions )
so that the resulting parentheses string is valid and return any valid string.
Formally, a parentheses string is valid if and only if:
- It is the empty string, contains only lowercase characters, or
- It can be written as
AB(A concatenated with B), where A and B are valid strings, or - It can be written as
(A), where A is a valid string.
Test Cases
Example 1:
Input: s = "lee(t(c)o)de)"
Output: "lee(t(c)o)de"
Explanation: "lee(t(co)de)" , "lee(t(c)ode)" would also be accepted.
Example 2:
Input: s = "))(("
Output: ""
Explanation: An empty string is also valid.
Solution
class Solution {
public:
string minRemoveToMakeValid(string s) {
stack<int> st;
int n = s.length();
for(int i=0; i<n; i++) {
if (s[i] == '(') {
st.push(i);
} else if (s[i] == ')') {
if (!st.empty()) {
st.pop();
} else {
s[i] = '*';
}
}
}
while(!st.empty()) {
s[st.top()] = '*';
st.pop();
}
s.erase(remove(s.begin(), s.end(), '*'), s.end());
return s;
}
};class Solution {
public String minRemoveToMakeValid(String s) {
StringBuilder builder = new StringBuilder(s);
Deque<Integer> stack = new ArrayDeque<>();
for(int i=0; i<s.length(); i++) {
char c = s.charAt(i);
if (c == '(') {
stack.offerLast(i);
} else if (c == ')') {
if (!stack.isEmpty()) {
stack.pollLast();
} else {
builder.setCharAt(i, '*');
}
}
}
while(!stack.isEmpty()) {
builder.setCharAt(stack.pollLast(), '*');
}
return builder.toString().replace("*", "");
}
}
/*
* Alternate approach without using stack
class Solution {
public String minRemoveToMakeValid(String s) {
StringBuilder sb = new StringBuilder(s);
int open = 0;
for(int i=0; i<s.length(); i++) {
char c = s.charAt(i);
if (c == '(') {
open++;
} else if (c == ')') {
if (open > 0) {
open--;
} else {
sb.setCharAt(i, '*');
}
}
}
int i = s.length() - 1;
while(i >=0 && open > 0) {
if (s.charAt(i) == '(') {
sb.setCharAt(i, '*');
open--;
}
i--;
}
return sb.toString().replace("*", "");
}
}
*
* */class Solution:
def minRemoveToMakeValid(self, s: str) -> str:
stack = []
arr = list(s)
print(arr)
for i in range(len(s)):
if s[i] == '(':
stack.append(i)
elif s[i] == ')':
if not stack:
arr[i] = '*'
else:
stack.pop()
while stack:
arr[stack.pop()] = '*'
return ''.join(arr).replace('*', '')