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Nora's solution to the challenge.

Don't look at this before you've completed the challenge!

This is not the only correct solution, just one example.
I have notated the solution with comments beginning with NORA
to help explain my reasoning and the purpose of each line.
solution
Leonora Tindall 11 months ago
parent
commit
1cbd2e725a
Signed by: nora GPG Key ID: 7A8B52EC67E09AAF
  1. 45
      src/lib.rs

45
src/lib.rs

@ -11,6 +11,8 @@ use std::io::Write;
pub struct Parser {
token: &'static [u8],
suffix: &'static [u8],
/// NORA: Records the position in the token across calls to `process`.
pos: usize,
}
impl Parser {
@ -19,7 +21,11 @@ impl Parser {
//
// NOTE: This function signature should stay the same.
pub fn new(token: &'static [u8], suffix: &'static [u8]) -> Self {
Self { token, suffix }
Self {
token,
suffix,
pos: 0,
}
}
/// Write the bytes given in `input` to `output`, plus the bytes in `suffix`
@ -56,7 +62,42 @@ impl Parser {
//
// NOTE: This function signature should stay the same.
pub fn process(&mut self, input: &[u8], output: &mut dyn Write) -> Result<(), std::io::Error> {
output.write_all(input)
// NORA: Create a buffer to work in for just this call.
// We'll write the whole buffer at the end, unconditionally;
// the only question is what's in it.
let mut buffer = Vec::with_capacity(input.len() + self.suffix.len());
// NORA: Look at each byte in the input.
for byte in input {
// NORA: Unconditionally, write that byte into our buffer.
// No requirement calls for losing any bytes.
buffer.push(*byte);
// NORA: Compare the current byte in the input to the current byte
// in the token.
if *byte == self.token[self.pos] {
// NORA: If this byte is a match, progress to the next token byte.
self.pos += 1;
// NORA: If we've reached the end of the token,
// that's a successful match.
if self.pos == self.token.len() {
// NORA: Write the whole suffix into the output buffer.
for suffix_byte in self.suffix {
buffer.push(*suffix_byte);
}
// NORA: And reset to zero, so we can look for a new match.
self.pos = 0;
}
} else {
// NORA: If the current input byte isn't a match for the current
// token byte, we have failed to match the token;
// reset to the beginning.
// This prevents e.g. "oat meal" from matching "oatmeal".
self.pos = 0;
}
}
output.write_all(&buffer)
}
}

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