Merge pull request #33 from naminodarie/feature/next_permutation

NextPermutationの仕様を変更

AtCoderLibrary.Test/Math/MathLibTest.cs

@@ -185,8 +185,7 @@ public void CRTBound()
                 }
             }
 
-            var factorInf = new long[] { 49, 73, 127, 337, 92737, 649657 };
-            do
+            foreach (var factorInf in StlFunction.NextPermutation(new long[] { 49, 73, 127, 337, 92737, 649657 }))
             {
                 foreach (long ans in pred)
                 {
@@ -200,10 +199,9 @@ public void CRTBound()
                     var res = MathLib.CRT(r.ToArray(), m.ToArray());
                     res.Should().Be((ans % INF, INF));
                 }
-            } while (NextPermutation(factorInf));
+            }
 
-            var factorInfn1 = new long[] { 2, 3, 715827883, 2147483647 };
-            do
+            foreach (var factorInfn1 in StlFunction.NextPermutation(new long[] { 2, 3, 715827883, 2147483647 }))
             {
                 foreach (long ans in pred)
                 {
@@ -217,12 +215,6 @@ public void CRTBound()
                     var res = MathLib.CRT(r.ToArray(), m.ToArray());
                     res.Should().Be((ans % (INF - 1), INF - 1));
                 }
-            } while (NextPermutation(factorInfn1));
-
-            static bool NextPermutation(long[] arr)
-            {
-                Skip.If(true, "NextPermutation is not implemented.");
-                throw new Exception(arr.ToString());
             }
         }
     }

AtCoderLibrary/STL/StlFunction.cs

@@ -1,32 +1,59 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 
 namespace AtCoder
 {
     public static class StlFunction
     {
-        /// <summary>
-        /// 辞書順によるその次の順列を生成します。返すインスタンスは共通です。
-        /// </summary>
-        public static IEnumerable<T[]> NextPermutation<T>(IEnumerable<T> orig) where T : IComparable<T>
+        public struct NextPermutationEnumerator<T> : IEnumerator<T[]>, IEnumerable<T[]> where T : IComparable<T>
         {
-            var arr = orig.ToArray();
-            while (true)
+            private readonly IEnumerable<T> _orig;
+            internal NextPermutationEnumerator(IEnumerable<T> orig)
+            {
+                _orig = orig;
+                Current = null;
+            }
+
+            public T[] Current { get; private set; }
+
+            public bool MoveNext()
             {
-                yield return arr;
+                if (Current == null)
+                {
+                    Current = _orig.ToArray();
+                    return true;
+                }
+
+                var arr = Current;
+
                 int i;
                 for (i = arr.Length - 2; i >= 0; i--)
                     if (arr[i].CompareTo(arr[i + 1]) < 0)
                         break;
-                if (i < 0) break;
+                if (i < 0)
+                    return false;
                 int j;
                 for (j = arr.Length - 1; j >= 0; j--)
                     if (arr[i].CompareTo(arr[j]) < 0)
                         break;
                 (arr[i], arr[j]) = (arr[j], arr[i]);
                 Array.Reverse(arr, i + 1, arr.Length - i - 1);
+                return true;
             }
+            public void Reset() => Current = null;
+            object IEnumerator.Current => Current;
+            void IDisposable.Dispose() { }
+            public NextPermutationEnumerator<T> GetEnumerator() => this;
+            IEnumerator<T[]> IEnumerable<T[]>.GetEnumerator() => this;
+            IEnumerator IEnumerable.GetEnumerator() => this;
         }
+
+        /// <summary>
+        /// 辞書順によるその次の順列を生成します。返すインスタンスは共通です。
+        /// </summary>
+        public static NextPermutationEnumerator<T> NextPermutation<T>(IEnumerable<T> orig) where T : IComparable<T>
+            => new NextPermutationEnumerator<T>(orig);
     }
 }