Algorithms and Data Structures

N.Wirth. Algorithms and Data Structures. Oberon version 48
k := (i+j) DIV 2;
IF x < a[k] THEN j := k-1 END;
IF a[k] < x THEN i := k+1 END
UNTIL i > j
Program C:
i := 0; j := N-1;
REPEAT
k := (i+j) DIV 2;
IF x < a[k] THEN j := k ELSE i := k+1 END
UNTIL i > j
Hint: All programs must terminate with a k = x, if such an element exists, or a k ≠ x, if there exists no
element with value x.
1.7. A company organizes a poll to determine the success of its products. Its products are records and
tapes of hits, and the most popular hits are to be broadcast in a hit parade. The polled population is to be
divided into four categories according to sex and age (say, less or equal to 20, and older than 20). Every
person is asked to name five hits. Hits are identified by the numbers 1 to N (say, N = 30). The results of the
poll are to be appropriately encoded as a sequence of characters.
Hint: use procedures Read and ReadInt to read the values of the poll.
TYPE hit = INTEGER;
reponse = RECORD name, firstname: Name;
male: BOOLEAN;
age: INTEGER;
choice: ARRAY 5 OF hit
END;
VAR poll: Files.File
This file is the input to a program which computes the following results:
1. A list of hits in the order of their popularity. Each entry consists of the hit number and the number of
times it was mentioned in the poll. Hits that were never mentioned are omitted from the list.
2. Four separate lists with the names and first names of all respondents who had mentioned in first place
one of the three hits most popular in their category.
The five lists are to be preceded by suitable titles.
References
[1.1] O-.J. Dahl, E.W. Dijkstra, C.A.R. Hoare. Structured Programming. F. Genuys, Ed., New York,
Academic Press, 1972.
[1.2] C.A.R. Hoare, in Structured Programming [1.1], pp. 83-174.
[1.3] K. Jensen and N. Wirth. PASCAL — User Manual and Report. Springer-Verlag, 1974.
[1.4] N. Wirth. Program development by stepwise refinement. Comm. ACM, 14, No. 4 (1971), 221-27.
[1.5] N. Wirth. Programming in Modula-2. Springer-Verlag, 1982.
[1.6] N. Wirth. On the composition of well-structured programs. Computing Surveys, 6, No. 4, (1974)
247-59.
[1.7] C.A.R. Hoare. The Monitor: An operating systems structuring concept. Comm. ACM 17, 10 (Oct.