# Quick Sort in Algol68

Published on 29 January 2023 (Updated: 31 January 2023)

Welcome to the Quick Sort in Algol68 page! Here, you'll find the source code for this program as well as a description of how the program works.

## Current Solution

``````MODE PARSEINT_RESULT = STRUCT(BOOL valid, INT value, STRING leftover);
MODE PARSEINTLIST_RESULT = STRUCT(BOOL valid, REF []INT values);

PROC parse int = (REF STRING s) PARSEINT_RESULT:
(
BOOL valid := FALSE;
REAL r := 0.0;
INT n := 0;
STRING leftover;

# Associate string with a file #
FILE f;
associate(f, s);

# On end of input, exit if valid number not seen. Otherwise ignore it #
on logical file end(f, (REF FILE dummy) BOOL:
(
IF NOT valid THEN done FI;
TRUE
)
);

# Exit if value error #
on value error(f, (REF FILE dummy) BOOL: done);

# Convert string to real number #
get(f, r);

# If real number is in range of an integer, convert to integer. Indicate integer is valid if same as real #
IF ABS r <= max int
THEN
n := ENTIER(r);
valid := (n = r)
FI;

# Get leftover string #
get(f, leftover);

done:
close(f);
PARSEINT_RESULT(valid, n, leftover)
);

PROC count list items = (STRING s) INT:
(
INT count := 1;
FOR k TO UPB s
DO
IF s[k] = ","
THEN
count +:= 1
FI
OD;

count
);

PROC parse int list = (REF STRING s) PARSEINTLIST_RESULT:
(
BOOL valid := FALSE;
STRING leftover := s;
INT num list items = count list items(s);
HEAP [num list items]INT values;

# Repeat while valid value #
FOR k TO num list items
DO
# Get next integer value and update leftover string #
PARSEINT_RESULT result = parse int(leftover);
valid := valid OF result;
leftover := leftover OF result;

# Append the integer value to list #
values[k] := value OF result;

# Do nothing if end of string #
IF leftover = ""
THEN
SKIP
# Skip comma if leftover string starts with comma #
ELIF leftover[1] = ","
THEN
leftover := leftover[2:]
# Otherwise indicate invalid #
ELSE
valid := FALSE
FI
UNTIL NOT valid
OD;

PARSEINTLIST_RESULT(valid, values)
);

PROC usage = VOID: (
printf((\$gl\$, "Usage: please provide a list of at least two integers to sort in the format ""1, 2, 3, 4, 5"""))
);

COMMENT
Source: https://en.wikipedia.org/wiki/Quicksort#Lomuto_partition_scheme
COMMENT
PROC quick sort = (REF []INT values) VOID:
(
quick sort rec(values, 1, UPB values)
);

PROC quick sort rec = (REF []INT values, INT lo, INT hi) VOID:
(
IF lo < hi AND lo >= 1
THEN
# Partition array and get pivot value #
INT p := partition(values, lo, hi);

# Sort left side of partition #
quick sort rec(values, lo, p - 1);

# Sort right side of partition #
quick sort rec(values, p + 1, hi)
FI
);

PROC partition = (REF []INT values, INT lo, INT hi) INT:
(
# Choose last value as pivot #
INT pivot = values[hi];

# Set temporary pivot index #
INT i := lo - 1;

# Swap elements less than or equal to pivot, and increment temporary index #
FOR j FROM lo TO hi - 1
DO
IF values[j] <= pivot
THEN
i +:= 1;
swap(values, i, j)
FI
OD;

# Move pivot to correct position #
i +:= 1;
swap(values, i, hi);

i
);

PROC swap = (REF []INT values, INT a, INT b) VOID:
(
INT temp := values[a];
values[a] := values[b];
values[b] := temp
);

PROC show list values = (REF []INT values) VOID:
(
INT n = UPB values;
FOR k TO n
DO
IF k > 1
THEN
print(", ")
FI;

print(whole(values[k], 0))
OD;

IF n > 0
THEN
print(newline)
FI
);

# Parse 1st command-line argument #
STRING s := argv(4);
PARSEINTLIST_RESULT list result := parse int list(s);
REF []INT values := values OF list result;
IF NOT valid OF list result OR UPB values < 2
THEN
usage;
stop
FI;

# Do quick sort and show results #
quick sort(values);
show list values(values)

``````

Quick Sort in Algol68 was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

## How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

## How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.