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Display a linear combination: Difference between revisions
Add Rust implementation
(Add Rust implementation) |
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Line 1,597:
[-1, -2, 0, -3] -> -e(1) - 2*e(2) - 3*e(4)
[-1] -> -e(1)</pre>
=={{header|Rust}}==
<lang rust>
use std::fmt::{Display, Formatter, Result};
use std::process::exit;
struct Coefficient(usize, f64);
impl Display for Coefficient {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
let i = self.0;
let c = self.1;
if c == 0. {
return Ok(());
}
write!(
f,
" {} {}e({})",
if c < 0. {
"-"
} else if f.alternate() {
" "
} else {
"+"
},
if (c.abs() - 1.).abs() < f64::EPSILON {
"".to_string()
} else {
c.abs().to_string() + "*"
},
i + 1
)
}
}
fn usage() {
println!("Usage: display-linear-combination a1 [a2 a3 ...]");
}
fn linear_combination(coefficients: &[f64]) -> String {
let mut string = String::new();
let mut iter = coefficients.iter().enumerate();
// find first nonzero argument
loop {
match iter.next() {
Some((_, &c)) if c == 0. => {
continue;
}
Some((i, &c)) => {
string.push_str(format!("{:#}", Coefficient(i, c)).as_str());
break;
}
None => {
string.push('0');
return string;
}
}
}
// print subsequent arguments
for (i, &c) in iter {
string.push_str(format!("{}", Coefficient(i, c)).as_str());
}
string
}
fn main() {
let mut coefficients = Vec::new();
let mut args = std::env::args();
args.next(); // drop first argument
// parse arguments into floats
for arg in args {
let c = arg.parse::<f64>().unwrap_or_else(|e| {
eprintln!("Failed to parse argument \"{}\": {}", arg, e);
exit(-1);
});
coefficients.push(c);
}
// no arguments, print usage and exit
if coefficients.is_empty() {
usage();
return;
}
println!("{}", linear_combination(&coefficients));
}
</lang>
{{out}}
<pre>
1 2 3 -> e(1) + 2*e(2) + 3*e(3)
</pre>
=={{header|Scala}}==
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