[leetcode] Remove Invalid Parentheses

Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results.

Note: The input string may contain letters other than the parentheses ( and ).

Examples:
"()())()" -> ["()()()", "(())()"]
"(a)())()" -> ["(a)()()", "(a())()"]
")(" -> [""]

"())()"

去掉1个    "))()"     "()()"   "()()"    "()))"        "())("

去掉2个  ")()"      .................................

................

public List<String> removeInvalidParentheses(String s) {
List<String> result = new ArrayList<String>();
Set<String> hs = new HashSet<String>();
Queue<String> queue = new LinkedList<String>();
boolean find = false;
queue.offer(s);
hs.add(s);
while (! queue.isEmpty()) {
String str = queue.poll();
if (isValid(str)) {
result.add(str);
find = true;
}
if (find) {
continue;
}
for (int i = 0; i < str.length(); i++) {
if (str.charAt(i) != '(' && str.charAt(i) != ')') {
continue;
}
String tmp = str.substring(0, i) + str.substring(i + 1);
if (! hs.contains(tmp)) { //记录已经添加到队列的元素，防止重复计算。
hs.add(tmp);
queue.offer(tmp);
}
}
}
return result;
}
public boolean isValid(String str) {
int count = 0;
for (int i = 0; i < str.length(); i++) {
if (str.charAt(i) == '(') {
count++;
} else if (str.charAt(i) == ')') {
if (count > 0) {
count--;
} else {
return false;
}
}
}
return count == 0;
}