First Non-Repeating Value

Find the first input value whose final frequency is one.

Algorithm

Canonical input [3, 5, 2, 5, 3, 8, 2] prints 8. The replay uses the same input in every language, so this Bash DSA implementation can be compared directly with the rest of the DSA track.

Basic Implementation

basic.sh

#!/usr/bin/env bash
arr=(3 5 2 5 3 8 2)
declare -A count=()
for value in "${arr[@]}"; do
  count[$value]=$(( ${count[$value]:-0} + 1 ))
done
for value in "${arr[@]}"; do
  if [[ ${count[$value]} -eq 1 ]]; then
    echo "$value"
    break
  fi
done

Complexity

Time: O(n) average
Space: O(k) for k distinct values

Implementation notes

Keep output formatting deterministic. Do not rely on unordered hash-map printing when the lesson needs cross-language comparison.
The trace highlights the hash table state after each write.

two-pass lookup The first pass builds a frequency table. The second pass keeps the original order and stops at the first value with frequency one.