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

```
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 usage = VOID: printf(($gl$, "Usage: please input the total number of people and number of people to skip."));
COMMENT
Reference: https://en.wikipedia.org/wiki/Josephus_problem#The_general_case
Use zero-based index algorithm:
g(1, k) = 0
g(m, k) = [g(m - 1, k) + k] MOD m, for m = 2, 3, ..., n
Final answer is g(n, k) + 1 to get back to one-based index
COMMENT
PROC josephus = (INT n, INT k) INT:
(
INT g := 0;
FOR m FROM 2 TO n
DO
g := (g + k) MOD m
OD;
g + 1
);
# Parse 1st and 2nd command-line arguments #
[2]INT values;
FOR m TO 2
DO
STRING s := argv(m + 3);
PARSEINT_RESULT result := parse int(s);
# If invalid, extra characters, exit #
values[m] := value OF result;
IF NOT (valid OF result) OR (leftover OF result) /= ""
THEN
usage;
stop
FI
OD;
INT n := values[1];
INT k := values[2];
INT g := josephus(n, k);
printf(($gl$, whole(g, 0)))
```

Josephus Problem in Algol68 was written by:

- rzuckerm

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

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

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