Array of Doubled Pairs LeetCode solution in Rust

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use std::collections::*;
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impl Solution {
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  pub fn can_reorder_doubled(arr: Vec<i32>) -> bool {
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    let mut btreemap = BTreeMap::new();
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    let mut count = 0;
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    for v in arr {
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      if v != 0 {
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        count += 1;
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        *btreemap.entry(v).or_insert(0) += 1;
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      }
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    }
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    if count % 2 == 1 {
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      return false;
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    }
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    while btreemap.keys().len() > 0 {
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      let (&val, &num) = btreemap.iter().next().unwrap();
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      let tval = if val < 0 {
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        if val % 2 != 0 {
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          return false;
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        }
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        val / 2
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      } else {
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        val * 2
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      };
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      if let Some(num) = btreemap.get_mut(&tval) {
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        if *num == 1 {
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          btreemap.remove(&tval);
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        } else {
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          *num -= 1;
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        }
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      } else {
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        return false;
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      }
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      if num == 1 {
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        btreemap.remove(&val);
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      } else {
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        btreemap.insert(val, num - 1);
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      }
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    }
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    true
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  }
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}