Data commit

Task/Stern-Brocot-sequence/PL-I/stern-brocot-sequence.pli

@@ -0,0 +1,48 @@
+sternBrocot: procedure options(main);
+    %replace MAX by 1200;
+    declare S(1:MAX) fixed;
+
+    /* find the first occurrence of N in S */
+    findFirst: procedure(n) returns(fixed);
+        declare (n, i) fixed;
+        do i=1 to MAX;
+            if S(i)=n then return(i);
+        end;
+    end findFirst;
+
+    /* find the greatest common divisor of A and B */
+    gcd: procedure(a, b) returns(fixed) recursive;
+        declare (a, b) fixed;
+        if b = 0 then return(a);
+        return(gcd(b, mod(a, b)));
+    end gcd;
+
+    /* calculate S(i) up to MAX */
+    declare i fixed;
+    S(1) = 1; S(2) = 1;
+    do i=2 to MAX/2;
+        S(i*2-1) = S(i) + S(i-1);
+        S(i*2) = S(i);
+    end;
+
+    /* print first 15 elements */
+    put skip list('First 15 elements: ');
+    do i=1 to 15;
+        put edit(S(i)) (F(2));
+    end;
+
+    /* find first occurrences of 1..10 and 100 */
+    do i=1 to 10;
+        put skip list('First',i,'at',findFirst(i));
+    end;
+    put skip list('First   ',100,'at',findFirst(100));
+
+    /* check GCDs of adjacent pairs up to 1000th element */
+    do i=2 to 1000;
+        if gcd(S(i-1),S(i)) ^= 1 then do;
+            put skip list('GCD of adjacent pair not 1 at i=',i);
+            stop;
+        end;
+    end;
+    put skip list('All GCDs of adjacent pairs are 1.');
+end sternBrocot;