[LeetCode]301. Remove Invalid Parentheses

https://leetcode.com/problems/remove-invalid-parentheses/?tab=Description

用最少的操作，得到括号为valid的所有结果

用found记录是否已经找到过结果了，如果已经找到过了就不再对当前str进行分解。visit记录已访问过的，queue记录待访问的。

public class Solution {
    public List removeInvalidParentheses(String s) {
        List res = new LinkedList();
        Queue queue = new LinkedList();
        HashSet visit = new HashSet();
        boolean found = false;
        queue.offer(s);
        visit.add(s);
        while (!queue.isEmpty()) {
            String str = queue.poll();
            if (valid(str)) {
                res.add(str);
                found = true;
            }
            if (found) {
                continue;
            }
            for (int i = 0; i < str.length(); i++) {
                char c = str.charAt(i);
                if (c != '(' && c != ')') {
                    continue;
                }
                String temp = str.substring(0, i) + str.substring(i + 1);
                if (!visit.contains(temp)) {
                    queue.add(temp);
                    visit.add(temp);
                }
            }
        }
        return res;
    }
    private boolean valid(String s) {
        int count = 0;
        for (int i = 0; i < s.length() && count >= 0; i++) {
            char c = s.charAt(i);
            if (c == '(') {
                count++;
            } else if (c == ')') {
                count--;
            }
        }
        return count == 0;
    }
}