diff --git a/source/implement_strstr/mod.rs b/source/implement_strstr/mod.rs
new file mode 100644
index 0000000..e4f3fc9
--- /dev/null
+++ b/source/implement_strstr/mod.rs
@@ -0,0 +1,14 @@
+pub fn str_str(haystack: String, needle: String) -> i32 {
+  if needle.is_empty() {
+    return 0;
+  }
+
+  haystack.find(&needle).map(|n| n as i32).unwrap_or(-1)
+}
+
+#[test]
+fn test_implement_strstr() {
+  assert_eq!(str_str("hello".to_string(), "ll".to_string()), 2);
+  assert_eq!(str_str("aaaaa".to_string(), "bba".to_string()), -1);
+  assert_eq!(str_str("aaaaa".to_string(), "".to_string()), 0);
+}
diff --git a/source/lib.rs b/source/lib.rs
index 7708af6..1ec11ef 100644
--- a/source/lib.rs
+++ b/source/lib.rs
@@ -1,3 +1,4 @@
+pub mod implement_strstr;
 pub mod longest_common_prefix;
 pub mod palindrome_number;
 pub mod reverse_integer;