add 1021

fishercoder1534 · fishercoder1534 · commit ce1cfeb21838 · 2019-04-07T08:11:46.000-07:00
diff --git a/README.md b/README.md
@@ -27,6 +27,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|---------------|---------------|--------|-------------|-------------
+|1021|[Remove Outermost Parentheses](https://leetcode.com/problems/remove-outermost-parentheses/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1021.java) | O(n) | O(n) | |Easy|
 |1018|[Binary Prefix Divisible By 5](https://leetcode.com/problems/binary-prefix-divisible-by-5/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1018.java) | O(n) | O(1) | |Easy|
 |1013|[Pairs of Songs With Total Durations Divisible by 60](https://leetcode.com/problems/pairs-of-songs-with-total-durations-divisible-by-60/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1013.java) | O(n) | O(1) | |Easy|
 |1002|[Find Common Characters](https://leetcode.com/problems/find-common-characters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1002.java) | O(n) | O(1) | |Easy|
diff --git a/src/main/java/com/fishercoder/solutions/_1021.java b/src/main/java/com/fishercoder/solutions/_1021.java
@@ -0,0 +1,68 @@
+package com.fishercoder.solutions;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**1021. Remove Outermost Parentheses
+ *
+ * A valid parentheses string is either empty (""), "(" + A + ")", or A + B, where A and B are valid parentheses strings, and + represents string concatenation.  For example, "", "()", "(())()", and "(()(()))" are all valid parentheses strings.
+ *
+ * A valid parentheses string S is primitive if it is nonempty, and there does not exist a way to split it into S = A+B, with A and B nonempty valid parentheses strings.
+ *
+ * Given a valid parentheses string S, consider its primitive decomposition: S = P_1 + P_2 + ... + P_k, where P_i are primitive valid parentheses strings.
+ *
+ * Return S after removing the outermost parentheses of every primitive string in the primitive decomposition of S.
+ *
+ *
+ * Example 1:
+ * Input: "(()())(())"
+ * Output: "()()()"
+ * Explanation:
+ * The input string is "(()())(())", with primitive decomposition "(()())" + "(())".
+ * After removing outer parentheses of each part, this is "()()" + "()" = "()()()".
+ *
+ * Example 2:
+ * Input: "(()())(())(()(()))"
+ * Output: "()()()()(())"
+ * Explanation:
+ * The input string is "(()())(())(()(()))", with primitive decomposition "(()())" + "(())" + "(()(()))".
+ * After removing outer parentheses of each part, this is "()()" + "()" + "()(())" = "()()()()(())".
+ *
+ * Example 3:
+ * Input: "()()"
+ * Output: ""
+ * Explanation:
+ * The input string is "()()", with primitive decomposition "()" + "()".
+ * After removing outer parentheses of each part, this is "" + "" = "".
+ *
+ * Note:
+ *
+ * S.length <= 10000
+ * S[i] is "(" or ")"
+ * S is a valid parentheses string
+ * */
+public class _1021 {
+    public static class Solution1 {
+        public String removeOuterParentheses(String S) {
+            List<String> primitives = new ArrayList<>();
+            for (int i = 1; i < S.length(); i++) {
+                int initialI = i - 1;
+                int left = 1;
+                while (i < S.length() && left > 0) {
+                    if (S.charAt(i) == '(') {
+                        left++;
+                    } else {
+                        left--;
+                    }
+                    i++;
+                }
+                primitives.add(S.substring(initialI, i));
+            }
+            StringBuilder sb = new StringBuilder();
+            for (String primitive : primitives) {
+                sb.append(primitive.substring(1, primitive.length() - 1));
+            }
+            return sb.toString();
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1021Test.java b/src/test/java/com/fishercoder/_1021Test.java
@@ -0,0 +1,32 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1021;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1021Test {
+    private static _1021.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1021.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals("()()()", solution1.removeOuterParentheses("(()())(())"));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals("()()()()(())", solution1.removeOuterParentheses("(()())(())(()(()))"));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals("", solution1.removeOuterParentheses("()()"));
+    }
+
+}
