September 2017 Update

Task/Permutations/Rust/permutations-1.rust

@@ -0,0 +1,34 @@
+struct QuickPerm<T> {
+    idxs: Vec<usize>,
+    elems: Vec<T>,
+    idx: usize,
+}
+
+impl<T: Clone> QuickPerm<T>  {
+    fn new(elems: Vec<T>) -> Self {
+        QuickPerm { idxs: (0..elems.len()+1).collect(), elems: elems, idx: 1 }
+    }
+}
+
+impl<T: Clone> Iterator for QuickPerm<T> {
+    type Item = Vec<T>;
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.idx == self.elems.len() { return None; }
+
+        self.idxs[self.idx] -= 1;
+        let other = if self.idx % 2 == 1 { self.idxs[self.idx] } else { 0 };
+        self.elems.swap(self.idx, other);
+        self.idx = 1;
+        while self.idxs[self.idx] == 0 {
+            self.idxs[self.idx] = self.idx;
+            self.idx += 1;
+        }
+        Some(self.elems.clone())
+    }
+}
+
+fn main() {
+    for perm in QuickPerm::new(vec![1,2,3]) {
+        println!("{:?}", perm);
+    }
+}