LeetCode:Remove Invalid Parentheses

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Remove Invalid Parentheses

Total Accepted: 14168 Total Submissions: 43620 Difficulty: Hard

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())()"]")(" -> [""]

Credits:
Special thanks to @hpplayer for adding this problem and creating all test cases.

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(E) Valid Parentheses

思路：

BFS

java code:

public class Solution {    public List<String> removeInvalidParentheses(String s) {                List<String> ans = new ArrayList<>();        if(s == null) return ans;                Set<String> visited = new HashSet<>();        Queue<String> queue = new LinkedList<>();        queue.offer(s);                boolean found = false;        while(!queue.isEmpty()) {                        String tmp = queue.poll();            if(isValid(tmp)) {                ans.add(tmp);                found = true;            }            if(found) continue;                        for(int i = 0;i < tmp.length();i++) { //将各个（去掉i字符的）子串入队                if(tmp.charAt(i) != '(' && tmp.charAt(i) != ')') continue;                String sub = tmp.substring(0,i) + tmp.substring(i+1);                                if(!visited.contains(sub)) {                    queue.offer(sub);                    visited.add(sub);                }            }        }        return ans;    }        // 自定义函数：检查是否合法    boolean isValid(String s) {        int count = 0;        for(int i=0;i<s.length();i++) {            char c = s.charAt(i);            if(c == '(') count++;            if(c == ')') {                if(count==0) return false;                count--;            }        }        return count == 0;    }}

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