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Question 1

What is the time complexity of accessing an element by its index in an array?

A

O(1)

B

O(n)

C

O(log n)

D

O(n²)

Question 2

What is the time complexity of searching for an element in a singly linked list?

A

O(1)

B

O(n)

C

O(log n)

D

O(n²)

Question 3

What is the space complexity of the following code that finds duplicates in an array using a HashSet?

import java.util.HashSet;

public class Solution {
    public boolean hasDuplicate(int[] arr) {
        HashSet<Integer> set = new HashSet<>();
        for (int num : arr) {
            if (set.contains(num)) {
                return true;
            }
            set.add(num);
        }
        return false;
    }
}

A

O(1)

B

O(n)

C

O(logn)

D

O(n²)

Question 4

What is the time complexity of the following code for reversing a linked list?

class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}

public class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode current = head;
        while (current != null) {
            ListNode nextNode = current.next;
            current.next = prev;
            prev = current;
            current = nextNode;
        }
        return prev;
    }
}

A

O(1)

B

O(n²)

C

O(n)

D

O(log n)

Question 5

What is the space complexity of the following code that checks for balanced parentheses using a stack?

import java.util.Stack;

public class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        for (char c : s.toCharArray()) {
            if (c == '(' || c == '{' || c == '[') {
                stack.push(c);
            } else {
                if (stack.isEmpty()) return false;
                char top = stack.pop();
                if ((c == ')' && top != '(') || 
                    (c == '}' && top != '{') || 
                    (c == ']' && top != '[')) {
                    return false;
                }
            }
        }
        return stack.isEmpty();
    }
}

A

O(n)

B

O(1)

C

O(log n)

D

O(n²)

Question 6

What is the time complexity of the following code that performs a depth-first traversal on a binary tree?

    public void dfs(TreeNode root) {
        if (root == null) return;
        System.out.println(root.val);
        dfs(root.left);
        dfs(root.right);
    }

A

O(1)

B

O(log n)

C

O(n²)

D

O(n)

.....

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