add 1541

fishercoder1534 · fishercoder1534 · commit 777f9dcee3be · 2020-08-08T10:33:51.000-07:00
diff --git a/README.md b/README.md
@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1541|[Minimum Insertions to Balance a Parentheses String](https://leetcode.com/problems/minimum-insertions-to-balance-a-parentheses-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1541.java) | |Medium|String, Stack|
 |1539|[Kth Missing Positive Number](https://leetcode.com/problems/kth-missing-positive-number/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1539.java) | |Easy|Array, HashTable|
 |1535|[Find the Winner of an Array Game](https://leetcode.com/problems/find-the-winner-of-an-array-game/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1535.java) | [:tv:](https://youtu.be/v6On1TQfMTU) |Medium|Array|
 |1534|[Count Good Triplets](https://leetcode.com/problems/count-good-triplets/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1534.java) | |Easy|Array|
diff --git a/src/main/java/com/fishercoder/solutions/_1541.java b/src/main/java/com/fishercoder/solutions/_1541.java
@@ -0,0 +1,59 @@
+package com.fishercoder.solutions;
+
+import java.util.Stack;
+
+public class _1541 {
+    public static class Solution1 {
+        public int minInsertions(String s) {
+            Stack<Character> stack = new Stack<>();
+            int insertionsNeeded = 0;
+            for (int i = 0; i < s.length(); i++) {
+                char c = s.charAt(i);
+                if (c == '(') {
+                    if (stack.isEmpty()) {
+                        stack.add(c);
+                    } else {
+                        if (stack.peek() == ')') {
+                            //in this case, we need to add one more ')' to get two consecutive right paren, then we could pop the one ')' and one '(' off the stack
+                            insertionsNeeded++;
+                            stack.pop();
+                            stack.pop();
+                            stack.add(c);
+                        } else {
+                            stack.add(c);
+                        }
+                    }
+                } else if (c == ')') {
+                    if (stack.isEmpty()) {
+                        //in this case, we need to add one '(' before we add this ')' onto this stack
+                        insertionsNeeded++;
+                        stack.add('(');
+                        stack.add(c);
+                    } else {
+                        if (stack.peek() == ')') {
+                            //in this case, we could pop the one ')' and one '(' off the stack
+                            stack.pop();
+                            stack.pop();
+                        } else {
+                            stack.add(c);
+                        }
+                    }
+                }
+            }
+            if (stack.isEmpty()) {
+                return insertionsNeeded;
+            } else {
+                while (!stack.isEmpty()) {
+                    char pop = stack.pop();
+                    if (pop == '(') {
+                        insertionsNeeded += 2;
+                    } else {
+                        insertionsNeeded++;
+                        stack.pop();
+                    }
+                }
+                return insertionsNeeded;
+            }
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1541Test.java b/src/test/java/com/fishercoder/_1541Test.java
@@ -0,0 +1,47 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1541;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1541Test {
+    private static _1541.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1541.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(1, solution1.minInsertions("(()))"));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(0, solution1.minInsertions("())"));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(3, solution1.minInsertions("))())("));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(12, solution1.minInsertions("(((((("));
+    }
+
+    @Test
+    public void test5() {
+        assertEquals(5, solution1.minInsertions(")))))))"));
+    }
+
+    @Test
+    public void test6() {
+        assertEquals(4, solution1.minInsertions("(()))(()))()())))"));
+    }
+
+}
