#19: add solution for exercise #22 in rust

rust/backtracking/0022-generate-parentheses.rs

@@ -0,0 +1,22 @@
+impl Solution {
+    pub fn generate_parenthesis(n: i32) -> Vec<String> {
+        fn gen(s: String, open: i32, closed: i32) -> Vec<String> {
+            let mut answers = vec![];
+            if open == 0 && closed == 0 {
+                return vec![s];
+            }
+
+            if open > 0 {
+                answers.append(&mut gen(s.clone()+"(", open-1, closed+1));
+            }
+
+            if closed > 0 {
+                answers.append(&mut gen(s.clone()+")", open, closed-1));
+            }
+
+            answers
+        }
+
+        gen("".to_string(), n, 0)
+    }
+}