Function condense 

pub fn condense(str: &str) -> String

Removes all duplicate characters from a string, preserving the first occurrence of each.

This function iterates through the input string and builds a new string containing only the first occurrence of each character, maintaining the original order. It uses a HashSet to track which characters have already been encountered.

Algorithm

1. Create an empty HashSet to track seen characters
2. Create an empty result String
3. For each character in the input:
   • If the character hasn’t been seen (insert returns true), append it to the result
   • If the character has been seen (insert returns false), skip it
4. Return the result string

Arguments

• str - A string slice to be condensed

Returns

A new String with all duplicate characters removed, preserving the order of first occurrences

Examples

use old_crypto_rs::helpers::condense;

// Simple duplicates
let result = condense("AAAAA");
assert_eq!(result, "A");

// Mixed duplicates
let result = condense("ARABESQUE");
assert_eq!(result, "ARBESQU");

// Longer string with duplicates
let result = condense("ARABESQUEABCDEFGHIKLMNOPQRSTUVWXYZ");
assert_eq!(result, "ARBESQUCDFGHIKLMNOPTVWXYZ");

// No duplicates
let result = condense("ABCDE");
assert_eq!(result, "ABCDE");

Performance

Time complexity: O(n) where n is the length of the input string Space complexity: O(k) where k is the number of unique characters

See Also

• condense_str - An optimized version using a bitset for ASCII characters