Data commit

Task/Permutations-by-swapping/Rust/permutations-by-swapping.rust

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+// Implementation of Heap's algorithm.
+// See https://en.wikipedia.org/wiki/Heap%27s_algorithm#Details_of_the_algorithm
+fn generate<T, F>(a: &mut [T], output: F)
+where
+    F: Fn(&[T], isize),
+{
+    let n = a.len();
+    let mut c = vec![0; n];
+    let mut i = 1;
+    let mut sign = 1;
+    output(a, sign);
+    while i < n {
+        if c[i] < i {
+            if (i & 1) == 0 {
+                a.swap(0, i);
+            } else {
+                a.swap(c[i], i);
+            }
+            sign = -sign;
+            output(a, sign);
+            c[i] += 1;
+            i = 1;
+        } else {
+            c[i] = 0;
+            i += 1;
+        }
+    }
+}
+
+fn print_permutation<T: std::fmt::Debug>(a: &[T], sign: isize) {
+    println!("{:?} {}", a, sign);
+}
+
+fn main() {
+    println!("Permutations and signs for three items:");
+    let mut a = vec![0, 1, 2];
+    generate(&mut a, print_permutation);
+
+    println!("\nPermutations and signs for four items:");
+    let mut b = vec![0, 1, 2, 3];
+    generate(&mut b, print_permutation);
+}