diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index 92659b1..b7bcd4e 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -165,4 +165,5 @@ mod p127_word_ladder;
 mod p208_implement_trie_prefix_tree;
 mod p211_design_add_and_search_words_data_structure;
 mod p212_word_search_ii;
-mod p17_letter_combinations_of_a_phone_number;
\ No newline at end of file
+mod p17_letter_combinations_of_a_phone_number;
+mod p77_combinations;
\ No newline at end of file
diff --git a/src/problem/p77_combinations.rs b/src/problem/p77_combinations.rs
new file mode 100644
index 0000000..225ca5c
--- /dev/null
+++ b/src/problem/p77_combinations.rs
@@ -0,0 +1,45 @@
+/**
+ * [77] Combinations
+ */
+pub struct Solution {}
+
+
+// submission codes start here
+
+impl Solution {
+    pub fn combine(n: i32, k: i32) -> Vec<Vec<i32>> {
+        let mut result = vec![];
+        let mut now = Vec::with_capacity(k as usize);
+
+        Self::search(n, k, 1, &mut now, &mut result);
+
+        result
+    }
+
+    fn search(n: i32, k: i32, x: i32, now: &mut Vec<i32>, result: &mut Vec<Vec<i32>>) {
+        if now.len() as i32 + (n - x + 1) < k {
+            return;
+        }
+
+        if now.len() as i32 >= k {
+            result.push(now.clone());
+            return;
+        }
+
+        now.push(x);
+        Self::search(n, k, x + 1, now, result);
+        now.pop();
+        Self::search(n, k, x + 1, now, result);
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_77() {
+    }
+}