diff --git a/src/main.rs b/src/main.rs
index 294b626..4cbbdad 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,28 +1,57 @@
+use std::collections::HashSet;
+
 mod arr;
 mod list;
 
 struct Solution {}
 impl Solution {
-    pub fn remove_outer_parentheses(s: String) -> String {
-        let mut cnt = 0;
-        let mut ans = vec![];
-        for c in s.chars() {
-            if c == '(' {
-                if cnt != 0 {
-                    ans.push(c);
-                }
-                cnt += 1;
-            } else {
-                cnt -= 1;
-                if cnt != 0 {
-                    ans.push(c);
+    pub fn remove_invalid_parentheses(s: String) -> Vec<String> {
+        let s = s.as_bytes().to_vec();
+        let mut queue1 = HashSet::new();
+        fn valid(x: &Vec<u8>) -> bool {
+            let mut cnt = 0;
+            for c in x {
+                if *c == b'(' {
+                    cnt += 1;
+                } else if *c == b')' {
+                    cnt -= 1;
+                    if cnt < 0 {
+                        return false;
+                    }
                 }
             }
+            cnt == 0
+        }
+        queue1.insert(s);
+        loop {
+            {
+                let mut local_ans = vec![];
+                for x in queue1.iter() {
+                    if valid(&x) {
+                        local_ans.push(x.clone());
+                    }
+                }
+                if !local_ans.is_empty() {
+                    return local_ans
+                        .into_iter()
+                        .map(|x| x.iter().map(|&y| y as char).collect::<String>())
+                        .collect();
+                }
+            }
+            let mut queue2 = HashSet::<Vec<u8>>::new();
+            for x in queue1.into_iter(){
+                for i in 0..x.len() {
+                    queue2.insert( x[..i].iter().chain(x[i + 1..].iter()).copied().collect());
+                }
+            }
+            queue1 = queue2;
         }
-        ans.iter().collect()
     }
 }
 
 fn main() {
-    println!("{:?}", Solution::remove_outer_parentheses("(()())(())(()(()))".to_string()));
+    println!(
+        "{:?}",
+        Solution::remove_invalid_parentheses(")()())()))(((()()()(()".to_string())
+    );
 }