Weekly Coding Challenge #4

Given two strings s and t, return true if t is an anagram of s (same letters, same counts, any order), otherwise false.

Examples

• s = "anagram", t = "nagaram" → true
• s = "rat", t = "car" → false

Constraints

• 1 <= s.length, t.length <= 5 * 10^4
• s and t consist of lowercase English letters.

Follow-up: what if the inputs contain Unicode characters? How would you adapt your solution?

Why this pattern matters

Counting item frequencies is everywhere: bag-of-words and token counts in NLP, near-duplicate and plagiarism detection, log analysis, and fraud checks. Frequency maps turn "are these the same?" into a cheap comparison.

Solution to Challenge #3: Contains Duplicate

Problem: given an integer array nums, return true if any value appears at least twice, otherwise false.

Approach: brute force compares every pair, O(n²). Instead, scan once and remember what you've seen in a HashSet. add() returns false when the value is already present, so the first repeat ends the search.

import java.util.HashSet;
import java.util.Set;

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Set<Integer> seen = new HashSet<>();

        for (int num : nums) {
            if (!seen.add(num)) {
                return true;
            }
        }
        return false;
    }
}