add lc company, update progress

yennanliu · Jun 10, 2024 · 03b4171 · 03b4171
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diff --git a/data/progress.txt b/data/progress.txt
@@ -1,3 +1,4 @@
+20240610:
 20240609: 236(again*),1448(again),needcode_trie,208(ok*),needcode_graph,695,22(todo),981(todo),207(todo),261(todo)
 20240608: 503(todo),739(ok),105(todo),needcode_heap_pq,1046,215,needcode_backtrack,78,39(todo),46,90(todo),77
 20240607: 235(ok),236(again),496(ok),110(ok),1448(again!)

diff --git a/doc/Leetcode_company_frequency-master/100 Most Asked Problems - LeetCode.pdf b/doc/Leetcode_company_frequency-master/100 Most Asked Problems - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/100 Most Liked Problems - LeetCode.pdf b/doc/Leetcode_company_frequency-master/100 Most Liked Problems - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Adobe - LeetCode alltime.pdf b/doc/Leetcode_company_frequency-master/Adobe - LeetCode alltime.pdf
diff --git a/doc/Leetcode_company_frequency-master/Adobe - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Adobe - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Aetion - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Aetion - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Affirm - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Affirm - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Airbnb - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Airbnb - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Akuna Capital - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Akuna Capital - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Alibaba - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Alibaba - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/All Problems sorted by frequency- LeetCode.pdf b/doc/Leetcode_company_frequency-master/All Problems sorted by frequency- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Amazon - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Amazon - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Amazon 1year- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Amazon 1year- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Amazon 6months- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Amazon 6months- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/AppDynamics - LeetCode.pdf b/doc/Leetcode_company_frequency-master/AppDynamics - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Apple - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Apple - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Asana - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Asana - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Atlassian - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Atlassian - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Audible - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Audible - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Baidu - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Baidu - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Barclays - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Barclays - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Bloomberg - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Bloomberg - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Booking.com - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Booking.com - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Box - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Box - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/ByteDance - LeetCode.pdf b/doc/Leetcode_company_frequency-master/ByteDance - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Capital One - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Capital One - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Cisco - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Cisco - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Citadel - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Citadel - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Citrix - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Citrix - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Cohesity - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Cohesity - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Coupang - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Coupang - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Coursera - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Coursera - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Cruise Automation - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Cruise Automation - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Databricks - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Databricks - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/DoorDash - LeetCode.pdf b/doc/Leetcode_company_frequency-master/DoorDash - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Dropbox - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Dropbox - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Evernote - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Evernote - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Expedia - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Expedia - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Facebook - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Facebook - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Facebook 1year- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Facebook 1year- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Facebook 6months- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Facebook 6months- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Flipkart - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Flipkart - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/GoDaddy - LeetCode.pdf b/doc/Leetcode_company_frequency-master/GoDaddy - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Goldman Sachs - LeetCode alltime.pdf b/doc/Leetcode_company_frequency-master/Goldman Sachs - LeetCode alltime.pdf
diff --git a/doc/Leetcode_company_frequency-master/Goldman Sachs - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Goldman Sachs - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Google - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Google - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Google 1year- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Google 1year- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Google 6months- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Google 6months- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Grab - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Grab - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Groupon - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Groupon - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Houzz - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Houzz - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Huawei - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Huawei - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Hulu - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Hulu - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/IBM - LeetCode.pdf b/doc/Leetcode_company_frequency-master/IBM - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/IXL - LeetCode.pdf b/doc/Leetcode_company_frequency-master/IXL - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Indeed - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Indeed - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Intel - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Intel - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Intuit - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Intuit - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/JPMorgan - LeetCode.pdf b/doc/Leetcode_company_frequency-master/JPMorgan - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/LinkedIn - LeetCode alltime.pdf b/doc/Leetcode_company_frequency-master/LinkedIn - LeetCode alltime.pdf
diff --git a/doc/Leetcode_company_frequency-master/LinkedIn - LeetCode.pdf b/doc/Leetcode_company_frequency-master/LinkedIn - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/LiveRamp - LeetCode.pdf b/doc/Leetcode_company_frequency-master/LiveRamp - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Lyft - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Lyft - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Mathworks - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Mathworks - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Microsoft - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Microsoft - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Microsoft 1year- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Microsoft 1year- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Microsoft 6months- LeetCode.pdf b/doc/Leetcode_company_frequency-master/Microsoft 6months- LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Morgan Stanley - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Morgan Stanley - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/NetEase - LeetCode.pdf b/doc/Leetcode_company_frequency-master/NetEase - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Netflix - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Netflix - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Nutanix - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Nutanix - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Nvidia - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Nvidia - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Opendoor - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Opendoor - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Oracle - LeetCode alltime.pdf b/doc/Leetcode_company_frequency-master/Oracle - LeetCode alltime.pdf
diff --git a/doc/Leetcode_company_frequency-master/Oracle - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Oracle - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Palantir Technologies - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Palantir Technologies - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Paypal - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Paypal - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Pinterest - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Pinterest - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Pocket Gems - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Pocket Gems - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Pure Storage - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Pure Storage - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Qualcomm - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Qualcomm - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Qualtrics - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Qualtrics - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Quip (Salesforce) - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Quip (Salesforce) - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Quora - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Quora - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/README.md b/doc/Leetcode_company_frequency-master/README.md
diff --git a/doc/Leetcode_company_frequency-master/Reddit - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Reddit - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Redfin - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Redfin - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Robinhood - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Robinhood - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Roblox - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Roblox - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Rubrik - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Rubrik - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/SAP - LeetCode.pdf b/doc/Leetcode_company_frequency-master/SAP - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Salesforce - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Salesforce - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Samsung - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Samsung - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Snapchat - LeetCode alltime.pdf b/doc/Leetcode_company_frequency-master/Snapchat - LeetCode alltime.pdf
diff --git a/doc/Leetcode_company_frequency-master/Snapchat - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Snapchat - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Splunk - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Splunk - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Spotify - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Spotify - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Square - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Square - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Summary/leetcode Notes.pdf b/doc/Leetcode_company_frequency-master/Summary/leetcode Notes.pdf
diff --git a/doc/Leetcode_company_frequency-master/Sumologic - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Sumologic - LeetCode.pdf
diff --git a/...e Big Ideas Behind Reliable, Scalable, and Maintainable Systems-O’Reilly Media (2017).pdf b/...e Big Ideas Behind Reliable, Scalable, and Maintainable Systems-O’Reilly Media (2017).pdf
diff --git a/doc/Leetcode_company_frequency-master/Tableau - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Tableau - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Tencent - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Tencent - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Tesla - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Tesla - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/TripAdvisor - LeetCode.pdf b/doc/Leetcode_company_frequency-master/TripAdvisor - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/TripleByte - LeetCode.pdf b/doc/Leetcode_company_frequency-master/TripleByte - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Twilio - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Twilio - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Twitch - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Twitch - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Twitter - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Twitter - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Two Sigma - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Two Sigma - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Uber - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Uber - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/VMware - LeetCode.pdf b/doc/Leetcode_company_frequency-master/VMware - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Visa - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Visa - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Walmart Labs - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Walmart Labs - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Wayfair - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Wayfair - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Wish - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Wish - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Yahoo - LeetCode alltime.pdf b/doc/Leetcode_company_frequency-master/Yahoo - LeetCode alltime.pdf
diff --git a/doc/Leetcode_company_frequency-master/Yahoo - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Yahoo - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Yandex - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Yandex - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Yelp - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Yelp - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Zenefits - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Zenefits - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Zillow - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Zillow - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/Zulily - LeetCode.pdf b/doc/Leetcode_company_frequency-master/Zulily - LeetCode.pdf
diff --git a/doc/Leetcode_company_frequency-master/eBay - LeetCode.pdf b/doc/Leetcode_company_frequency-master/eBay - LeetCode.pdf
diff --git a/leetcode_java/src/main/java/dev/workSpace4.java b/leetcode_java/src/main/java/dev/workSpace4.java
@@ -246,6 +246,33 @@ public static void main(String[] args) {
         workSpace4 wp = new workSpace4();
         wp.myFunc();
 
+
+        System.out.println("isValidP test --------------");
+        String mystr = "(())"; //"()))";
+        System.out.println(wp.isValidP(mystr));
+
+    }
+
+    public boolean isValidP(String input){
+        System.out.println("---> input = " + input);
+        if (input.length() == 0){
+            return true;
+        }
+        // leftCnt : "(" count
+        // rightCnt : ") count
+        int leftCnt = 0;
+        int rightCnt = 0;
+        for (String x : input.split("")){
+            if (x.equals("(")){
+                leftCnt += 1;
+            }else{
+                rightCnt += 1;
+            }
+            if (rightCnt > leftCnt){
+                return false;
+            }
+        }
+        return true;
     }
 
     private void myFunc(){

diff --git a/leetcode_java/src/main/java/dev/workspace3.java b/leetcode_java/src/main/java/dev/workspace3.java
@@ -4804,5 +4804,92 @@ public void getBiggestArea(int x, int y, int[][] grid, int curArea) {
         //return curArea;
     }
 
+    // LC 22
+    // IDEA : Backtrack
+    // 1 <= n <= 8
+    // 3.30
+    List<String> res_ = new ArrayList<>();
+    public List<String> generateParenthesis2(int n) {
+
+        //List<String> res = new ArrayList<>();
+        if (n == 1){
+            this.res_.add("(");
+            this.res_.add(")");
+            return this.res_;
+        }
+
+        // backtrack
+        String cur = "";
+        this.getParenthesis_(n, cur);
+        System.out.println("this.res_ = " + this.res_);
+        return this.res_;
+    }
+
+    // leftCnt : "(" count
+    // rightCnt : ") count
+    public void getParenthesis_(int n, String cur) {
+
+        if (cur.length() > 2 * n){
+            return;
+        }
+
+        if (isValidP(cur.toString()) && cur.toString().length() == 2 * n) {
+            if (!this.res_.contains(cur)) {
+                this.res_.add(cur);
+                cur = ""; // ?
+                return;
+            }
+        }
+
+        String[] choices = {"(", ")"};
+        StringBuilder sb = new StringBuilder(cur);
+        for (String c : choices) {
+            /**
+             *  2 conditions
+             *
+             *  1)  leftCnt > rightCnt
+             *  2)  1st element must be "("
+             *
+             */
+            // case 1) invalid string
+            if (!isValidP(cur)) {
+                return;
+            }
+
+            // case 2) cur is null
+            if (sb.length() == 0) {
+                sb.append("(");
+            }else{
+                // case 3) OK to append "(" or ")"
+                sb.append(c);
+            }
+            // undo
+            this.getParenthesis_(n, sb.toString());
+            sb.deleteCharAt(sb.length() - 1);
+        }
+    }
+
+    public boolean isValidP(String input){
+        if (input.length() == 0){
+            return true;
+        }
+        // leftCnt : "(" count
+        // rightCnt : ") count
+        int leftCnt = 0;
+        int rightCnt = 0;
+        for (String x : input.split("")){
+            if (x.equals("(")){
+                leftCnt += 1;
+            }else{
+                rightCnt += 1;
+            }
+            if (rightCnt > leftCnt){
+                return false;
+            }
+        }
+        return true;
+    }
+
+
 
 }