Valid Anagram

Introduction

Strings are one of the most important topics in programming.
A common problem is checking whether two strings are anagrams, which means they contain the same characters in a different order.

Problem Statement

Given two strings s and t, return:

• true if t is an anagram of s
• false otherwise

Note:

• Both strings contain only lowercase English letters

Examples

Example 1:
Input: s = "anagram", t = "nagaram"
Output: true

Example 2:
Input: s = "rat", t = "car"
Output: false

Intuition

• If two strings are anagrams:

  • They must have the same characters
  • With the same frequency

Approach (Frequency Count)

Instead of sorting, we count occurrences of each character.

Algorithm Steps

• If lengths are different → return false
• Create a frequency array of size 26

• Traverse both strings:

  • Increment count for s[i]
  • Decrement count for t[i]

• If all values are 0 → anagram

Code (Python)

def is_anagram(s, t):
    if len(s) != len(t):
        return False

    count = [0] * 26

    for i in range(len(s)):
        count[ord(s[i]) - ord('a')] += 1
        count[ord(t[i]) - ord('a')] -= 1

    return all(c == 0 for c in count)

Step-by-Step Explanation

For "anagram" and "nagaram":

• Count characters in both strings
• Each increment cancels with decrement
• Final array → all zeros → valid anagram

Complexity Analysis

• Time Complexity: O(n)
• Space Complexity: O(1) (fixed 26 letters)

Conclusion

Checking for anagrams is a fundamental string problem that teaches frequency counting and efficient comparison techniques.