From ed450df09489f1cde664c203fc3a303080c042c1 Mon Sep 17 00:00:00 2001
From: uesugi6111 <59960488+uesugi6111@users.noreply.github.com>
Date: Sat, 2 Dec 2023 15:06:19 +0000
Subject: [PATCH 1/2] impl

---
 src/math/permutation.rs | 55 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/src/math/permutation.rs b/src/math/permutation.rs
index 496895d..32a49fd 100644
--- a/src/math/permutation.rs
+++ b/src/math/permutation.rs
@@ -37,6 +37,45 @@ 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 +84,20 @@ 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]);
+        }
+    }
 }

From 2c0507ec042f037ff2cbd9376baefa0bbb5e038e Mon Sep 17 00:00:00 2001
From: uesugi6111 <59960488+uesugi6111@users.noreply.github.com>
Date: Sat, 2 Dec 2023 15:56:17 +0000
Subject: [PATCH 2/2] format

---
 src/math/permutation.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/math/permutation.rs b/src/math/permutation.rs
index 32a49fd..62b0731 100644
--- a/src/math/permutation.rs
+++ b/src/math/permutation.rs
@@ -68,7 +68,9 @@ where
             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 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();