Longest Word in Dictionary LeetCode solution in Rust

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impl Solution {
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  pub fn longest_word(words: Vec<String>) -> String {
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    let mut m = std::collections::HashMap::new();
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    for w in words {
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      m.entry(w.len()).or_insert(Vec::new()).push(w);
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    }
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    let mut cur = 2_usize;
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    let mut level = Vec::new();
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    if let Some(v) = m.get(&1) {
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      level = v.clone();
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    } else {
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      return String::new();
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    }
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    loop {
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      let mut new_level = Vec::new();
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      if let Some(v) = m.get(&cur) {
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        for word in v {
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          if level.iter().any(|w| word.starts_with(w)) {
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            new_level.push(word.clone());
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          }
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        }
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      }
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      if new_level.is_empty() {
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        return level.iter().min().unwrap().to_string();
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      }
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      level = new_level;
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      cur += 1;
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    }
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  }
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}