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Quote:

Block 2 will run faster and use less performance compared to Block 1.

In Block 1, you are using a List<string> to combine the elements from two lists (a1 and a2) into a single list (combinedList). The code iterates over the length of the longer list (maxLength) and checks if the current index is within the bounds of each list before adding the element to the combinedList. Finally, it uses string.Join to concatenate the elements in combinedList into a single string.

In Block 2, you are using a StringBuilder (output) to build the combined string directly. The code iterates over the length of a1 and adds each element to the output. It also checks if the current index is within the bounds of a2 and adds its corresponding element. Finally, it prints the output using Console.WriteLine.

Block 2 is more efficient because it eliminates the need for an additional list (combinedList). It directly builds the string using StringBuilder, which is more efficient for concatenating multiple strings compared to repeatedly appending to a List<string>. Additionally, it does not involve the overhead of checking list bounds for every iteration, as it directly uses the lengths of a1 and a2 in the loop condition.