diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index 288ee4e..c8bf1df 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -126,4 +126,5 @@ mod p383_ransom_note;
 mod p290_word_pattern;
 mod p205_isomorphic_strings;
 mod p242_valid_anagram;
-mod p49_group_anagrams;
\ No newline at end of file
+mod p49_group_anagrams;
+mod p202_happy_number;
\ No newline at end of file
diff --git a/src/problem/p202_happy_number.rs b/src/problem/p202_happy_number.rs
new file mode 100644
index 0000000..e2b33e0
--- /dev/null
+++ b/src/problem/p202_happy_number.rs
@@ -0,0 +1,54 @@
+/**
+ * [202] Happy Number
+ */
+pub struct Solution {}
+
+// submission codes start here
+use std::{collections::HashSet, ops::Add};
+
+impl Solution {
+    pub fn is_happy(n: i32) -> bool {
+        let mut s = HashSet::new();
+
+        let mut n = Solution::calculate_square(n);
+
+        while n != 1 {
+            dbg!(n);
+            if s.contains(&n) {
+                return false;
+            }
+
+            s.insert(n);
+
+            n = Solution::calculate_square(n);
+        }
+
+        true
+    }
+
+    fn calculate_square(n: i32) -> i32 {
+        let mut n = n;
+
+        let mut result = 0;
+
+        while n != 0 {
+            result += (n % 10).pow(2);
+            n = n / 10;
+        }
+
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_202() {
+        assert!(Solution::is_happy(19));
+        assert!(!Solution::is_happy(2));
+    }
+}