Merge Strings Alternately

Alternate while either string remains

Maintain indices i and j. While i < len(word1) or j < len(word2), append word1[i] when available and advance i, then append word2[j] when available and advance j. The OR condition is important: once the shorter string ends, the remaining suffix of the longer one must still be copied. A builder or character array avoids repeated immutable-string allocation.

Keep the explanation proportional

There is no need for recursion or a nested loop. Walk through unequal examples such as "ab" and "pqrs" to show the tail behavior, and clarify that character encoding assumptions follow the language's string model. Every character is appended exactly once, so time is O(m+n) and output space is O(m+n), excluding any implementation-specific builder capacity. This is also a chance to show clean bounds management rather than overengineering a straightforward task.