Added Happy Number

Author: ryanoneill

src/happy_number.rs

@@ -0,0 +1,56 @@
+use std::collections::HashSet;
+
+/// Write an algorithm to determine if a number `n` is happy.
+///
+/// A happy number is a number defined by the following process:
+///
+/// * Starting with any positive integer, replace the number by the sum of the
+///   squares of its digits.
+///
+/// * Repeat the process until the number equals 1 (where it will stay), or it
+///   loops endlessly in a cycle which does not include 1.
+///
+/// * Those numbers for which this process ends in 1 are happy.
+///
+/// Return `true` if `n` is a happy number, and `false` if not.
+struct Solution;
+
+impl Solution {
+
+    pub fn is_happy(n: i32) -> bool {
+        let mut num = n;
+        let mut seen = HashSet::new();
+
+        while !seen.contains(&num) && num != 1 {
+            seen.insert(num);
+            num = num.to_string()
+                .split("")
+                .map(|d| d.parse::<i32>().unwrap_or_default())
+                .map(|d| d * d)
+                .sum();
+        }
+
+        num == 1
+    }
+
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    #[test]
+    fn example_1() {
+        let n = 19;
+        let result = Solution::is_happy(n);
+        assert!(result);
+    }
+
+    #[test]
+    fn example_2() {
+        let n = 2;
+        let result = Solution::is_happy(n);
+        assert!(!result);
+    }
+
+}

src/lib.rs

@@ -92,6 +92,8 @@ pub mod house_robber; // 198
 pub mod binary_tree_right_side_view; // 199
 pub mod number_of_islands; // 200
 
+pub mod happy_number; // 202
+
 pub mod reverse_linked_list; // 206
 pub mod course_schedule; // 207