DSA curriculum

DSA practice

Short exercises. Try them first, open the hint if you are stuck, and the solution last.

Exercise 1
Reverse with a stack
Use an array as a stack to reverse the string "queue" and print the result.
Your solutionJavaScript
Editable codeconst word = "queue"; const stack = []; // push every letter, then pop them into result let result = ""; console.log(result);
Ctrl+Enter to run
Exercise 2
First duplicate
Write firstDuplicate(arr) that returns the first value seen twice, or -1. Use a Set so it is O(n).
Your solutionJavaScript
Editable codefunction firstDuplicate(arr) { // your code } console.log(firstDuplicate([3, 1, 4, 1, 5, 3]));
Ctrl+Enter to run
Exercise 3
Balanced brackets
Write isBalanced(s) for strings of ( and ). Return true when every ( is closed.
Your solutionJavaScript
Editable codefunction isBalanced(s) { // your code } console.log(isBalanced("(())")); console.log(isBalanced("(()"));
Ctrl+Enter to run