Data commit

Task/Display-a-linear-combination/Rust/display-a-linear-combination.rust

@@ -0,0 +1,91 @@
+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));
+}