Algorithms and Data Structures

N.Wirth. Algorithms and Data Structures. Oberon version 84
IF L < N THEN k1 := L ELSE k1 := N END;
K1 := k1;
FOR i := 0 TO k1-1 DO (*set input riders*)
Runs.Set(r[i], g[i])
END;
FOR i := 0 TO k1-1 DO (*set output riders*)
g[i] := Files.New(""); Files.Set(w[i], g[i], 0)
END;
(*merge from r[0] ... r[k1-1] to w[0] ... w[K1-1]*)
FOR i := 0 TO k1-1 DO t[i] := i END;
L := 0; (*nof runs merged*)
j := 0;
REPEAT (*merge on run from inputs to w[j]*)
INC(L); k2 := k1;
REPEAT (*select the minimal key*)
m := 0; min := r[t[0]].first; i := 1;
WHILE i < k2 DO
x := r[t[i]].first;
IF x < min THEN min := x; m := i END;
INC(i)
END;
Runs.copy(r[t[m]], w[j]);
IF r[t[m]].eof THEN (*eliminate this sequence*)
DEC(k1); DEC(k2);
t[m] := t[k2]; t[k2] := t[k1]
ELSIF r[t[m]].eor THEN (*close run*)
DEC(k2);
tx := t[m]; t[m] := t[k2]; t[k2] := tx
END
UNTIL k2 = 0;
INC(j);
IF j = K1 THEN j := 0 END
UNTIL k1 = 0
UNTIL L = 1;
RETURN g[0]
END BalancedMerge