June 2018 Update

Task/Permutations/Fortran/permutations-4.f

@@ -0,0 +1,41 @@
+      program nptest
+      integer n,i,a
+      logical nextp
+      external nextp
+      parameter(n=4)
+      dimension a(n)
+      do i=1,n
+      a(i)=i
+      enddo
+   10 print *,(a(i),i=1,n)
+      if(nextp(n,a)) go to 10
+      end
+
+      function nextp(n,a)
+      integer n,a,i,j,k,t
+      logical nextp
+      dimension a(n)
+      i=n-1
+   10 if(a(i).lt.a(i+1)) go to 20
+      i=i-1
+      if(i.eq.0) go to 20
+      go to 10
+   20 j=i+1
+      k=n
+   30 t=a(j)
+      a(j)=a(k)
+      a(k)=t
+      j=j+1
+      k=k-1
+      if(j.lt.k) go to 30
+      j=i
+      if(j.ne.0) go to 40
+      nextp=.false.
+      return
+   40 j=j+1
+      if(a(j).lt.a(i)) go to 40
+      t=a(i)
+      a(i)=a(j)
+      a(j)=t
+      nextp=.true.
+      end