Big O Practice: String Concat

def join_words(words):
    result = ''
    for w in words:
        result = result + w
    return result

Variables

• n - total length of the concatenated result

Explanation

Looks linear - one `+=` per word - but each concatenation copies the entire result so far because strings are immutable. Summing 1 + 2 + ... + n character copies is **O(n²)**. Final string holds `n` chars, **O(n)** space. The fix is `"".join(words)` / `words.join("")` which is O(n).

More Big O practice problems · Today's daily problem