diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index 1c2568a..8a0ec06 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -284,3 +284,5 @@ mod p684_redundant_connection;
 mod p685_redundant_connection_ii;
 
 mod p3211_generate_binary_strings_without_adjacent_zeros;
+
+mod p3216_lexicographically_smallest_string_after_a_swap;
diff --git a/src/problem/p3216_lexicographically_smallest_string_after_a_swap.rs b/src/problem/p3216_lexicographically_smallest_string_after_a_swap.rs
new file mode 100644
index 0000000..7034e4c
--- /dev/null
+++ b/src/problem/p3216_lexicographically_smallest_string_after_a_swap.rs
@@ -0,0 +1,46 @@
+/**
+ * [3216] Lexicographically Smallest String After a Swap
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn get_smallest_string(s: String) -> String {
+        let mut s: Vec<u32> = s.chars().map(|x| x.to_digit(10).unwrap()).collect();
+
+        for i in 0..s.len() - 1 {
+            if s[i] % 2 != s[i + 1] % 2 {
+                continue;
+            }
+
+            if s[i] > s[i + 1] {
+                let temp = s[i];
+                s[i] = s[i + 1];
+                s[i + 1] = temp;
+                break;
+            }
+        }
+
+        s.into_iter().map(|x| x.to_string()).collect()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_3216() {
+        assert_eq!(
+            "43520".to_owned(),
+            Solution::get_smallest_string("45320".to_owned())
+        );
+        assert_eq!(
+            "001".to_owned(),
+            Solution::get_smallest_string("001".to_owned())
+        );
+    }
+}