feat: add valid anagram problem

Author: bujosa

src/easy/readme.md

@@ -1044,3 +1044,30 @@ Put the code below in main.rs and run `cargo run`
   let result = easy::palindrome_linked_list::is_palindrome(head);
   println!("result: {}", result);
 ```
+
+# 242. Valid anagram
+
+## Description
+
+Given two strings s and t , write a function to determine if t is an anagram of s.
+
+## Examples
+
+```text
+Input: s = "anagram", t = "nagaram"
+
+Output: true
+
+Input: s = "rat", t = "car"
+
+Output: false
+```
+
+## How to Run in main.rs
+
+Put this code below in main.rs and run `cargo run`
+
+```rust
+  let result = easy::valid_anagram::is_anagram(String::from("anagram"), String::from("nagaram"));
+  println!("result: {:?}", result);
+```

src/easy/valid_anagram.rs

@@ -0,0 +1,47 @@
+#![allow(dead_code)]
+pub fn is_anagram(s: String, t: String) -> bool {
+    use std::collections::HashMap;
+
+    let mut s_map: HashMap<char, i32> = HashMap::new();
+    let mut t_map: HashMap<char, i32> = HashMap::new();
+
+    for c in s.chars() {
+        let count = s_map.entry(c).or_insert(0);
+        *count += 1;
+    }
+
+    for c in t.chars() {
+        let count = t_map.entry(c).or_insert(0);
+        *count += 1;
+    }
+
+    s_map == t_map
+}
+
+/*
+  Algorithm - Hashmap
+   - Use a hashmap to store the frequency of each character in the first string
+   - Iterate through the second string and decrement the frequency of each character
+   - If the frequency of a character is 0, remove it from the hashmap
+   - If the hashmap is empty, then the strings are anagrams
+   - This solution is O(n) time and O(n) space
+
+  Time Complexity - O(n)
+  Space Complexity - O(n)
+*/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_is_anagram() {
+        assert_eq!(
+            is_anagram("anagram".to_string(), "nagaram".to_string()),
+            true
+        );
+        assert_eq!(is_anagram("rat".to_string(), "car".to_string()), false);
+
+        assert_eq!(is_anagram("aacc".to_string(), "ccac".to_string()), false);
+    }
+}

src/readme.md

@@ -32,6 +32,7 @@
   - [x] [119. Pascal's triangle II](src/easy/pascals_triangle.rs)
   - [x] [217. Contains duplicate](src/easy/contains_duplicate.rs)
   - [x] [234. Palindrome linked list](src/easy/palindrome_linked_list.rs)
+  - [x] [242. Valid anagram](src/easy/valid_anagram.rs)
 - [ ] [Medium](src/medium)
   - [x] [2. Add two numbers](src/medium/add_two_numbers.rs)
   - [x] [15. Three sum](src/medium/three_sum.rs)

theory/categories/1.arrays_&_hashing/readme.md

@@ -66,7 +66,7 @@
 ## Problems
 
 - [x] [1. Contains Duplicate](https://leetcode.com/problems/contains-duplicate/) | Easy problem | [Solution](src/easy/contains_duplicate.rs)
-- [ ] [2. Valid Anagram](https://leetcode.com/problems/valid-anagram/) | Easy problem
+- [x] [2. Valid Anagram](https://leetcode.com/problems/valid-anagram/) | Easy problem | [Solution](src/easy/valid_anagram.rs)
 - [x] [3. Two Sum](https://leetcode.com/problems/two-sum/) | Easy problem | [Solution](src/easy/two_sum.rs)
 - [ ] [4. Group Anagrams](https://leetcode.com/problems/group-anagrams/) | Medium Problem
 - [ ] [5. Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/) | Medium Problem