301. Remove Invalid Parentheses

每次remove一个( 或者 ) 看看整体valid吗 valid的话这个就是最小的remove数量 

 

class Solution {
    public List<String> removeInvalidParentheses(String s) {
        List<String> res = new ArrayList<>();
        Queue<String> queue = new LinkedList<>();
        Set<String> visited = new HashSet<>();
        queue.offer(s);
        visited.add(s);
        boolean found = false;
        while(!queue.isEmpty()){
            int size = queue.size();
            for(int i = 0; i < size; i++){
                String str = queue.poll();
                if(isValid(str)){
                    found = true;
                    res.add(str);
                }
                
                for(int j = 0; j < str.length(); j++){
                    if(!(str.charAt(j) == '(') && !(str.charAt(j) == ')')) continue;
                    String str1 = str.substring(0, j) + str.substring(j+1, str.length());
                    if(!visited.contains(str1)){
                        visited.add(str1);
                        queue.offer(str1);
                    }
                }
                
            }
            if(found) break;
            size = queue.size();
        }
        return res;  
    }
    
    public boolean isValid(String str){
        int count = 0;
        for(int i = 0; i < str.length(); i++){
            if(str.charAt(i) == '(') count++;
            if(str.charAt(i) == ')' && count-- == 0) return false;
        }
        return count == 0;
    }
}