java https://www.hrwhisper.me/leetcode-remove-invalid-parentheses/ http://blog.csdn.net/qq508618087/

Posted 2021-05-08

public class Solution {
    public List<String> removeInvalidParentheses(String s) {
        List<String> ans = new ArrayList<>();
        remove(s, ans, 0, 0, new char[]{'(', ')'});
        return ans;
    }
    
    public void remove(String s, List<String> ans, int last_i, int last_j,  char[] par) {
        for (int stack = 0, i = last_i; i < s.length(); ++i) {
            if (s.charAt(i) == par[0]) stack++;
            if (s.charAt(i) == par[1]) stack--;
            if (stack >= 0) continue;
            for (int j = last_j; j <= i; ++j)
                if (s.charAt(j) == par[1] && (j == last_j || s.charAt(j - 1) != par[1]))
                    remove(s.substring(0, j) + s.substring(j + 1, s.length()), ans, i, j, par);
            return;
        }
        String reversed = new StringBuilder(s).reverse().toString();
        if (par[0] == '(') // finished left to right
            remove(reversed, ans, 0, 0, new char[]{')', '('});
        else // finished right to left
            ans.add(reversed);
    }
}

sample 2 ms submission
public class Solution {
    public List<String> removeInvalidParentheses(String s) {
        List<String> ans = new ArrayList<>();
        removeLeft(s, ans, new char[s.length()], 0, 0, 0);
        return ans;
    }
    
    private static void removeLeft(String s, List<String> ans, char[] buf, int pos, int start, int last) {
        int p = start, b = 0;
        for (int i = start; i < s.length(); ++i) {
            if (s.charAt(i) == '(') {
                ++b;
            } else if (s.charAt(i) == ')') {
                --b;
            }
            if (b <= 0) {
                p = i + 1;
            }
            if (b < 0) {
                for (int j = last; j <= i; ++j) {
                    if (s.charAt(j) == ')' && (j == last || s.charAt(j - 1) != ')')) {
                        s.getChars(last, j, buf, pos);
                        removeLeft(s, ans, buf, pos + j - last, i + 1, j + 1);
                    }
                }
                return;
            }
        }
        s.getChars(last, p, buf, pos);
        int rem = b + (last - pos); // total number of parentheses to remove, including already removed
        removeRight(s, ans, buf, buf.length - rem, buf.length - rem, s.length() - 1, s.length() - 1, p);
    }
    
    private static void removeRight(String s, List<String> ans, char[] buf, int pos, int len,
            int start, int last, int p) {
        int b = 0;
        for (int i = start; i >= p; --i) {
            if (s.charAt(i) == ')') {
                ++b;
            } else if (s.charAt(i) == '(') {
                --b;
            }
            if (b < 0) {
                for (int j = last; j >= i; --j) {
                    if (s.charAt(j) == '(' && (j == last || s.charAt(j + 1) != '(')) {
                        s.getChars(j + 1, last + 1, buf, pos - (last - j));
                        removeRight(s, ans, buf, pos - (last - j), len, i - 1, j - 1, p);
                    }
                }
                return;
            }
        }
        s.getChars(p, last + 1, buf, pos - (last + 1 - p));
        ans.add(new String(buf, 0, len));
    }
}

public class Solution {
    public List<String> removeInvalidParentheses(String s) {
        List<String> res = new ArrayList<String>();
        //if(s == null || s.length() == 0) return res; "" ==> [""]
        if(s == null) return res;
        Queue<String> frontier = new LinkedList<String>();
        Set<String> explored = new HashSet<String>();
        
        frontier.offer(s);
        boolean flag = false; // stop exploring to next level after finding res in the current level
        while(!frontier.isEmpty()){
            String cur = frontier.poll();
            if(isValid(cur)) {
                res.add(cur);
                flag = true;
            }
            if(flag) {
                continue;
            }
            StringBuilder sb = new StringBuilder();
            sb.append(cur);
            for(int i = 0; i < cur.length(); i++){
                char temp = sb.charAt(i);
                if(temp == '(' || temp == ')') {
                    sb.deleteCharAt(i);
                    String nextStr = sb.toString();
                    if(!explored.contains(nextStr)) {
                        frontier.offer(nextStr);
                        explored.add(nextStr);
                    }
                    sb.insert(i, temp);
                }
                
            }
        }
        return res;
    }
    
    public boolean isValid(String str){
        int count = 0;
        for( int i = 0; i < str.length(); i++) {
            char temp = str.charAt(i);
            if (temp == '(') {
                count++;
            } else if (temp == ')') {
                if(count == 0) {
                    return false;
                }
                count--;
            }
        }
        return count == 0;
    }
}

/*
"()())()"
"(a)())()"
")("
""
*/