28 lines
662 B
Rust
28 lines
662 B
Rust
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pub fn max_value(mut n: isize, digit: char) -> Result<isize, String> {
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let digit = match digit.to_digit(10) {
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Some(d) => Ok(d as isize),
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None => Err("The digit is not valid"),
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}?;
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let negative = n < 0;
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if negative {
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n *= -1;
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}
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let nlen = (n.abs() as f32).log10().floor() as u32 + 1;
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let mut max = n * 10 + digit;
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let cmp = if negative {
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std::cmp::min
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} else {
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std::cmp::max
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};
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for i in 1..=nlen {
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let option = (n / 10isize.pow(i) * 10 + digit) * 10isize.pow(i) + n % 10isize.pow(i);
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max = cmp(max, option);
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}
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Ok(if negative { -max } else { max })
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}
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