Merge pull request #109 from uesugi6111/add-permutation-iter

add iter

src/math/permutation.rs

@@ -37,6 +37,47 @@ fn push_recusive<T: Clone>(
     vvec
 }
 
+pub struct Permutation<T>
+where
+    T: Clone,
+{
+    p: Vec<T>,
+    init: bool,
+}
+
+impl<T> Permutation<T>
+where
+    T: Clone,
+{
+    pub fn new(p: &[T]) -> Self {
+        Self {
+            p: p.to_vec(),
+            init: false,
+        }
+    }
+}
+impl<T> Iterator for Permutation<T>
+where
+    T: Clone + Ord,
+{
+    type Item = Vec<T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if !self.init {
+            self.p.sort();
+            self.init = true;
+            return Some(self.p.clone());
+        }
+        let Some(i) = (0..&self.p.len() - 1).rfind(|&i| self.p[i] < self.p[i + 1]) else {
+            return None;
+        };
+        let j = self.p.iter().rposition(|x| x > &self.p[i]).unwrap();
+        self.p.swap(i, j);
+        self.p[i + 1..].reverse();
+        Some(self.p.clone())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -45,4 +86,20 @@ mod tests {
         let vv = make_permutation(4);
         assert_eq!(0, vv[0][0]);
     }
+    #[test]
+    fn test_struct() {
+        let expect = [
+            &[0, 1, 2],
+            &[0, 2, 1],
+            &[1, 0, 2],
+            &[1, 2, 0],
+            &[2, 0, 1],
+            &[2, 1, 0],
+        ];
+        let a = Permutation::new(&[0, 1, 2]);
+
+        for (i, v) in a.enumerate() {
+            assert_eq!(v, expect[i]);
+        }
+    }
 }