feat: add initial implementation of happy number solution

202_happy_number/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "happy_number"
+version = "0.1.0"

202_happy_number/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "happy_number"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

202_happy_number/src/main.rs

@@ -0,0 +1,29 @@
+use std::collections::HashSet;
+
+fn main() {
+    println!("Hello, world!");
+}
+
+struct Solution;
+
+impl Solution {
+    pub fn is_happy(mut n: i32) -> bool {
+        let mut numbers_shown = HashSet::<i32>::new();
+        numbers_shown.insert(n);
+
+        while n != 1 {
+            let mut new_n = 0;
+            for c in n.to_string().chars() {
+                new_n += (c as i32 - 48).pow(2);
+            }
+            n = new_n;
+
+            if numbers_shown.contains(&n) {
+                return false;
+            }
+            numbers_shown.insert(n);
+        }
+
+        true
+    }
+}