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Welcome to the Longest Palindromic Substring in Algol68 page! Here, you’ll find the source code for this program as well as a description of how the program works.

```
COMMENT
Find longest palindromic string using matching array
Source: https://www.geeksforgeeks.org/longest-palindromic-substring-using-dynamic-programming/
COMMENT
PROC longest palindromic substring = (STRING s) STRING:
(
# Allocate array indicating whether there is a character match #
# between two characters #
INT n := UPB s;
HEAP [n, n]BOOL matches;
# Indicate all length 1 strings match and everything else does not #
FOR i TO n
DO
FOR j TO n
DO
matches[i, j] := FALSE
OD;
matches[i, i] := TRUE
OD;
# Convert string to lowercase #
STRING t;
FOR i TO n
DO
t +:= tolower(s[i])
OD;
# Find all length 2 matches #
INT start := 1;
INT max len := 1;
FOR i TO n - 1
DO
IF t[i] = t[i + 1]
THEN
matches[i, i + 1] := TRUE;
IF max len < 2
THEN
start := i;
max len := 2
FI
FI
OD;
# Find all length 3 or higher matches #
INT j;
FOR len FROM 3 TO n
DO
# Loop through each starting character #
FOR i TO n - len + 1
DO
# If match for one character in from start and end characters #
# and start and end characters match, set match for start and #
# end characters, and update max length #
j := i + len - 1;
IF matches[i + 1, j - 1] AND t[i] = t[j]
THEN
matches[i, j] := TRUE;
IF len > max len
THEN
max len := len;
start := i
FI
FI
OD
OD;
s[start:start + max len - 1]
);
PROC usage = VOID: printf(($gl$, "Usage: please provide a string that contains at least one palindrome"));
# Error if 1st command-line argument is missing is empty #
STRING s := argv(4);
IF UPB(s) = 0
THEN
usage;
stop
FI;
# Get longest palindromic substring. Error if none found #
STRING longest := longest palindromic substring(s);
IF UPB(longest) < 2
THEN
usage;
stop
FI;
# Show longest palindromic substring #
printf(($gl$, longest))
```

Longest Palindromic Substring 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.