05 August 2008
跟301的区别是这道题只需要返回一个有效的结果就行(301返回移除后所有的有效括号字符串)，同时可能不光是字符，额外Stack和Set记录哪些字符串可以删掉
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class Solution {
public String minRemoveToMakeValid(String s) {
if (s.isEmpty()) {
return "";
}
Set<Integer> indicesToRemove = new HashSet<>();
Stack<Integer> stack = new Stack<>();
for (int i = 0; i < s.length(); i++) {
char ch = s.charAt(i);
if (ch == '(') {
stack.push(i);
}
if (ch == ')') {
if (stack.isEmpty()) {
indicesToRemove.add(i);
} else {
stack.pop();
}
}
}
while (!stack.isEmpty()) { // some '(' left inside the stack
indicesToRemove.add(stack.pop());
}
StringBuilder sb = new StringBuilder();
for (int i = 0; i < s.length(); i++) {
if (!indicesToRemove.contains(i)) {
sb.append(s.charAt(i));
}
}
return sb.toString();
}
}