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impl Solution {
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  pub fn is_valid(code: String) -> bool {
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    Self::_is_valid(code.as_bytes()).unwrap_or(false)
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  }
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  fn _is_valid(code: &[u8]) -> Option<bool> {
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    let mut s = String::new();
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    let mut i = 0;
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    while i < code.len() {
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      if code[i] == b'<' && code.get(i + 1)? == &b'!' {
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        let mut t = String::new();
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        for (j, &item) in code.iter().enumerate().skip(i + 2) {
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          if j - i == 9 {
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            break;
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          }
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          t.push(item as char);
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        }
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        if t == "[CDATA[" || t == "[cdata[" {
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          i += 7;
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          while i < code.len() {
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            if code[i - 2] == b']' && code[i - 1] == b']' && code[i] == b'>' {
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              break;
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            }
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            i += 1;
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          }
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          s.push('#');
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        } else {
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          return Some(false);
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        }
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      } else {
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        s.push(code[i] as char);
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      }
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      i += 1;
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    }
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    let s = s.as_bytes();
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    if s.is_empty() || s[0] != b'<' {
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      return Some(false);
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    }
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    let mut st = Vec::new();
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    let mut k = 0;
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    let mut n = 0;
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    i = 0;
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    while i < s.len() {
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      if s[i] == b'<' {
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        let mut t = String::new();
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        n = 0;
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        if i == s.len() {
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          return Some(false);
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        }
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        if s.get(i + 1)? == &b'/' {
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          i += 2;
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          while i < s.len() {
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            let &s_i_byte = s.get(i)?;
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            if s_i_byte == b'>' {
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              break;
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            }
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            if !(b'A'..=b'Z').contains(&s_i_byte) {
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              return Some(false);
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            }
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            t.push(s_i_byte as char);
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            if t.len() == 10 {
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              return Some(false);
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            }
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            i += 1;
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          }
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          if st.is_empty() || st.pop().unwrap() != t {
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            return Some(false);
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          }
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        } else {
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          i += 1;
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          while i < s.len() {
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            let &s_i_byte = s.get(i)?;
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            if s_i_byte == b'>' {
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              break;
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            }
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            if !(b'A'..=b'Z').contains(&s_i_byte) {
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              return Some(false);
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            }
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            t.push(s_i_byte as char);
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            if t.len() == 10 {
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              return Some(false);
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            }
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            i += 1;
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          }
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          if t.is_empty()
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            || (st.is_empty() && {
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              k += 1;
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              k == 2
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            })
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          {
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            return Some(false);
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          }
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          st.push(t);
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        }
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      } else {
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        n = 1;
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      }
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      i += 1;
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    }
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    Some(st.is_empty() && n == 0)
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  }
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}