Data commit

Task/Modular-inverse/Lambdatalk/modular-inverse.lambdatalk

@@ -0,0 +1,32 @@
+{def mulinv
+ {def mulinv.loop
+  {lambda {:t :nt :r :nr}
+   {if {not {= :nr 0}}
+    then {mulinv.loop :nt
+                      {- :t {* {floor {/ :r :nr}} :nt}}
+                      :nr
+                      {- :r {* {floor {/ :r :nr}} :nr}} }
+    else {cons :t :r} }}}
+ {lambda {:a :n}
+  {let { {:a :a} {:n :n}
+         {:cons {mulinv.loop 0
+                             1
+                             {if {< :n 0} then {- :n} else :n}
+                             {if {< :a 0} then {- :n {% {- :a} :n}} else :a}}}
+       } {if {> {cdr :cons} 1}
+          then not invertible
+          else {if {< {car :cons} 0}
+          then {+ {car :cons} :n}
+          else {car :cons} }}}}}
+-> mulinv
+
+{mulinv 42 2017}
+-> 1969
+{mulinv 40 1}
+-> 0
+{mulinv 52 -217}
+-> 96
+{mulinv -486 217}
+-> 121
+{mulinv 40 218}
+-> not invertible