/// Determines whether all letters in `word` can be formed
/// from the letters available in `sentence`.
///
/// Rules:
/// - Letter order does not matter.
/// - Comparison is case-insensitive.
/// - Non-alphabetic characters are ignored.
///
/// # Arguments
///
/// * `sentence` - Source text containing available letters.
/// * `word` - Word to check.
///
/// # Returns
///
/// `true` if the word can be formed; otherwise `false`.
fn contains_word_letters(sentence: &str, word: &str) -> bool {
let mut available = [0_u32; 26];
// Count available letters in the sentence.
for ch in sentence.chars() {
let ch = ch.to_ascii_lowercase();
if ch.is_ascii_lowercase() {
available[(ch as u8 - b'a') as usize] += 1;
}
}
// Consume letters required by the word.
for ch in word.chars() {
let ch = ch.to_ascii_lowercase();
if !ch.is_ascii_lowercase() {
continue;
}
let index = (ch as u8 - b'a') as usize;
if available[index] == 0 {
return false;
}
available[index] -= 1;
}
true
}
fn main() {
let sentence = "Bright stars shine above calm valleys at night.";
println!(
"{}",
contains_word_letters(sentence, "satellite")
);
println!(
"{}",
contains_word_letters(sentence, "satellllite")
);
}
/*
run:
true
false
*/
