optimize 32

src/euler32/Cargo.toml

@@ -6,3 +6,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+
+[profile.release]
+debug = true
+lto = true

src/euler32/src/main.rs

@@ -1,42 +1,80 @@
 use std::collections::HashSet;
 
-type Int = u64;
+type Int = u32;
+
+const UPPER_BOUND: Int = 3_333; // because result must be a 4-digit number
 
 fn main() {
-    let f: Vec<_> = (1..10_000_u64)
+    let mut buffer1 = HashSet::new();
+    let mut buffer2 = HashSet::new();
+
+    let f = (1..UPPER_BOUND)
         .filter(|n| {
             let s = n.to_string();
             let hs = s.chars().collect::<HashSet<_>>();
             hs.len() == s.len() && !hs.contains(&'0')
         })
-        .collect();
+        .collect::<Vec<_>>()
+        .leak();
 
     let mut result = HashSet::new();
-    for f1 in &f {
-        for f2 in f.iter().rev() {
+    for f1 in f.iter() {
+        let lower_bound = UPPER_BOUND / f1;
+
+        'inner: for f2 in f.iter().skip_while(|i| **i < lower_bound) {
             let p = f1 * f2;
-            if are_pandigital([f1, f2, &p]) {
+            if f1.len() + f2.len() + p.len() > 9 {
+                break 'inner;
+            }
+
+            if are_pandigital([f1, f2, &p], &mut buffer1, &mut buffer2) {
                 println!("{f1} {f2} {p}");
                 result.insert(p);
             }
         }
     }
-    println!("{}", result.iter().sum::<u64>());
+    println!("{}", result.iter().sum::<Int>());
 }
 
-fn are_pandigital(input: [&Int; 3]) -> bool {
-    let mut accum = HashSet::new();
+fn are_pandigital(input: [&Int; 3], accum: &mut HashSet<char>, hs: &mut HashSet<char>) -> bool {
+    accum.clear();
+
     let mut length = 0;
+
     for n in input {
+        hs.clear();
+
         let s = n.to_string();
         length += s.len();
-        let hs = s.chars().collect::<HashSet<_>>();
+
+        s.chars().for_each(|c| {
+            hs.insert(c);
+        });
+
         if s.len() != hs.len() {
             return false;
         }
-        for item in hs {
-            accum.insert(item);
+
+        for item in hs.iter() {
+            accum.insert(*item);
         }
     }
+
     accum.len() == 9 && length == 9 && !accum.contains(&'0')
 }
+
+trait Length {
+    fn len(&self) -> usize;
+}
+
+impl Length for Int {
+    fn len(&self) -> usize {
+        let mut tmp = 1;
+        let mut oom = 1;
+        while tmp - 1 < *self {
+            oom += 1;
+            tmp *= 10;
+        }
+        oom - 1
+    }
+}