Decode Ways LeetCode solution in Rust

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impl Solution {
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  pub fn num_decodings(s: String) -> i32 {
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    let mut prev = 1;
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    let mut prev_2 = 0;
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    let mut prev_ch = 'X';
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    let mut cur = 1;
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    for ch in s.chars().rev() {
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      if ch == '1' || (ch == '2' && prev_ch as u8 <= '6' as u8) {
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        cur = prev_2 + prev;
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      } else if ch == '0' {
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        cur = 0;
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      }
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      prev_2 = prev;
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      prev = cur;
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      prev_ch = ch;
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    }
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    cur as _
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  }
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}