Rust - Use SmallVec for words instead of Vec.

src/rust/phone_encoder/Cargo.toml

@@ -10,6 +10,7 @@ license = ""
 [dependencies]
 #num-bigint = "0.4"
 num-bigint = { git = "https://github.com/rust-num/num-bigint.git", branch = "master" }
+smallvec = "1.6.1"
 
 [dev-dependencies]
 criterion = "0.3.5"

src/rust/phone_encoder/benches/bench1.rs

@@ -1,9 +1,10 @@
 use core::iter;
+use std::io::{self, BufWriter};
 
-use criterion::{BenchmarkId, Criterion, criterion_group, criterion_main, Throughput};
+use criterion::{BenchmarkId, black_box, Criterion, criterion_group, criterion_main, Throughput};
+use smallvec::SmallVec;
 
 use phone_encoder::print_solution;
-use std::io::{self, BufWriter};
 
 static NUM_SRC: [&str; 7] = ["123456", "78901234", "567890", "123456789", "012345", "43210", "98765432"];
 
@@ -38,5 +39,28 @@ fn bench_print_solution(c: &mut Criterion) {
     group.finish();
 }
 
-criterion_group!(benches, bench_print_solution);
+fn bench_vec_mut(c: &mut Criterion) {
+    let mut group = c.benchmark_group("vec_push_pop");
+    for words in [1, 10, 20, 30, 40, 50].iter()
+        .map(|size| generate_data(*size as usize, &WORD_SRC)) {
+        let size = words.len() as u64;
+        group.throughput(Throughput::Elements(size));
+        group.bench_with_input(BenchmarkId::from_parameter(size), &words, |b, words| {
+            b.iter(|| {
+                let mut vec = Vec::with_capacity(50);
+                for word in words {
+                    vec.push(black_box(word));
+                }
+                for _ in 0..words.len() {
+                    black_box(&vec);
+                    vec.pop();
+                }
+                vec
+            });
+        });
+    }
+    group.finish();
+}
+
+criterion_group!(benches, bench_vec_mut);
 criterion_main!(benches);

src/rust/phone_encoder/src/lib.rs

@@ -4,6 +4,7 @@ use std::io::{self, BufRead, Write};
 use std::path::Path;
 
 use num_bigint::BigUint;
+use smallvec::SmallVec;
 
 pub type Dictionary = HashMap<BigUint, Vec<String>>;
 
@@ -13,7 +14,7 @@ pub fn print_translations<'dict>(
     num: &str,
     digits: &[char],
     start: usize,
-    words: &mut Vec<&'dict str>,
+    words: &mut SmallVec<[&'dict str; 32]>,
     dict: &'dict Dictionary,
     writer: &mut impl Write,
 ) -> io::Result<()> {
@@ -46,7 +47,7 @@ pub fn print_translations<'dict>(
     }
 }
 
-pub fn print_solution(num: &str, words: &[&str], writer: &mut impl Write) {
+pub fn print_solution(num: &str, words: &SmallVec<[&str; 32]>, writer: &mut impl Write) {
     writeln!(writer, "{}: {}", num, words.join(" ")).expect("Cannot print solution");
 }
 

src/rust/phone_encoder/src/main.rs

@@ -1,5 +1,6 @@
 use std::env::args;
 use std::io::{self, BufWriter};
+use smallvec::SmallVec;
 
 mod lib;
 
@@ -22,7 +23,7 @@ fn main() -> io::Result<()> {
         let digits: Vec<_> = num.chars()
             .filter(|ch| ch.is_alphanumeric())
             .collect();
-        let mut words = Vec::new();
+        let mut words: SmallVec<[&str; 32]> = SmallVec::with_capacity(50);
         lib::print_translations(&num, &digits, 0, &mut words, &dict, &mut out)?;
     }
     Ok(())