Data commit

Task/Vampire-number/Rust/vampire-number.rust

@@ -0,0 +1,124 @@
+use std::cmp::{max, min};
+
+static TENS: [u64; 20] = [
+    1,
+    10,
+    100,
+    1000,
+    10000,
+    100000,
+    1000000,
+    10000000,
+    100000000,
+    1000000000,
+    10000000000,
+    100000000000,
+    1000000000000,
+    10000000000000,
+    100000000000000,
+    1000000000000000,
+    10000000000000000,
+    100000000000000000,
+    1000000000000000000,
+    10000000000000000000,
+];
+
+/// Get the number of digits present in x
+fn ndigits(mut x: u64) -> u64 {
+    let mut n = 0;
+
+    while x != 0 {
+        n += 1;
+        x /= 10;
+    }
+
+    n
+}
+
+fn dtally(mut x: u64) -> u64 {
+    let mut t = 0;
+
+    while x != 0 {
+        t += 1 << ((x % 10) * 6);
+        x /= 10;
+    }
+
+    t
+}
+
+/// Get a list of all fangs of x. Get only the first divider of each fang. The second one can be found simply with x / fang.
+fn fangs(x: u64) -> Vec<u64> {
+    let mut nd = ndigits(x) as usize;
+
+    let mut fangs = vec![];
+
+    if nd & 1 != 1 {
+        nd /= 2;
+
+        let lo = max(TENS[nd - 1], (x + TENS[nd] - 2) / (TENS[nd] - 1));
+        let hi = min(x / lo, (x as f64).sqrt() as u64);
+
+        let t = dtally(x);
+
+        for a in lo..(hi + 1) {
+            let b = x / a;
+            if a * b == x && ((a % 10) > 0 || b % 10 > 0) && t == dtally(a) + dtally(b) {
+                fangs.push(a);
+            }
+        }
+    }
+
+    fangs
+}
+
+/// Pretty print the fangs of x
+fn print_fangs(x: u64, fangs: Vec<u64>) {
+    print!("{} = ", x);
+
+    if fangs.is_empty() {
+        print!("is not vampiric");
+    } else {
+        for fang in fangs {
+            print!("{} x {}, ", fang, x / fang);
+        }
+    }
+    print!("\n");
+}
+
+fn main() {
+    println!("The first 25 vampire numbers are :");
+
+    let mut nfangs = 0;
+    let mut x = 1;
+
+    while nfangs < 25 {
+        let fangs = fangs(x);
+        if !fangs.is_empty() {
+            nfangs += 1;
+            print_fangs(x, fangs);
+        }
+
+        x += 1;
+    }
+
+    println!("\nSpecial requests :");
+
+    print_fangs(16758243290880, fangs(16758243290880));
+    print_fangs(24959017348650, fangs(24959017348650));
+    print_fangs(14593825548650, fangs(14593825548650));
+}
+
+#[test]
+fn test() {
+    assert_eq!(
+        fangs(16758243290880),
+        vec![1982736, 2123856, 2751840, 2817360]
+    );
+
+    assert_eq!(
+        fangs(24959017348650),
+        vec![2947050, 2949705, 4125870, 4129587, 4230765]
+    );
+
+    assert_eq!(fangs(14593825548650), vec![]);
+}