Added Java solution for "Minimum Add to Make Parentheses Valid"

Author: Kyrylo-Ktl

Java/Minimum Add to Make Parentheses Valid.java

@@ -0,0 +1,20 @@
+public class Solution {
+
+    /**
+     * Time:   O(n)
+     * Memory: O(1)
+     */
+    public int minAddToMakeValid(String s) {
+        int add = 0, score = 0;
+
+        for (int i = 0; i < s.length(); ++i) {
+            score += s.charAt(i) == '(' ? 1 : -1;
+            if (score == -1) {
+                ++add;
+                ++score;
+            }
+        }
+
+        return add + score;
+    }
+}