How to solve this java problem efficiently [closed]

Question

I am trying to solve this problem and I worked out a solution but its too slow, this is my approach:

1. loop to add all strings in an array
2. loop to concatenate strings based on inputs
3. print out final concatenated string

Which works, but I need a faster approach. I am thinking of trying to determine the order of concatenation of each string, then just print strings based on the order. But I have no idea how to determine the order in the first place. Does anyone have any advice? Thank you!

[SOLVED] thank you guys for the help! I was able to pass the test cases.

Answer 1

Java's strings are immutable. This means that each concatenation results in a fully new copy where both a and b are copied.

You need to use Java's StringBuilder and convert the end result to a normal string. StringBuilders truely append one to the other without copying the first one. They work like a dynamic length array under the hood.