Create 1021. Remove Outermost Parentheses

Author: haibarawu

1021. Remove Outermost Parentheses

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+/********** **********
+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
+********** **********/
+
+
+class Solution {
+    public String removeOuterParentheses(String S) {
+        int len = S.length();
+        int count = 0;
+        int begin = 0;
+        int end = 0;
+        StringBuilder s = new StringBuilder();
+        
+        for (int i = 0; i < len; i ++) {
+            char c = S.charAt(i);
+            if (c == '(') {
+                count ++;
+            }
+            else {
+                count --;
+            }
+            if (count == 0) {
+                end = i;
+                s.append(S.substring(begin + 1, end));
+                begin = end + 1;
+            }
+        }
+        
+        return s.toString();
+    }
+}