Generate Parentheses

GenerateParentheses/step1.md

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+```java
+// Until reach to the max length(n * 2)
+// We try to add left part first then add right side
+// Until number of left part reach to n, we can add left part
+// And if number of left part is bigger than right part, we can try to add right part
+// Time complexity: O(2**(N*2)) 
+// Space complexity: O(n) stack memory for backtack
+// Time spend: XX(Found the answer after checking Solutions tab)
+class Solution {
+    public List<String> generateParenthesis(int n) {
+        List<String> res = new ArrayList<>();
+        generateParenthesis(res, 0, 0, "", n);
+        return res;
+    }
+
+    public void generateParenthesis(List<String> res, int l, int r, String curr,int n) {
+        if (curr.length() == n * 2) {
+            res.add(curr);
+            return;
+        }
+
+        if (l < n) {
+            generateParenthesis(res, l + 1, r, curr + "(", n);
+        }
+        if (r < l) {
+            generateParenthesis(res, l, r + 1, curr + ")", n);
+        }
+    }
+}
+```

GenerateParentheses/step2.md

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+```java
+// Time spend: 01:47
+class Solution {
+    public List<String> generateParenthesis(int n) {
+        List<String> res = new ArrayList<>();
+        generateParenthesis(res, 0, 0, n, "");
+        return res;
+    }
+
+    public void generateParenthesis(List<String> res, int l, int r, int n, String curr) {
+        if (curr.length() == n * 2) {
+            res.add(curr);
+            return;
+        }
+
+        if (l < n) {
+            generateParenthesis(res, l + 1, r, n, curr + '(');
+        }
+
+        if (r < l) {
+            generateParenthesis(res, l, r + 1, n, curr + ')');
+        }
+    }
+}
+```

GenerateParentheses/step3.md

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+```java
+// Time spend: 01:33
+class Solution {
+    public List<String> generateParenthesis(int n) {
+        List<String> res = new ArrayList<>();
+        generateParenthesis(res, 0, 0, n, "");
+        return res;
+    }
+
+    public void generateParenthesis(List<String> res, int l, int r, int n, String curr) {
+        if (curr.length() == n * 2) {
+            res.add(curr);
+            return;
+        }
+
+        if (l < n) {
+            generateParenthesis(res, l + 1, r, n, curr + '(');
+        }
+
+        if (r < l) {
+            generateParenthesis(res, l, r + 1, n, curr + ')');
+        }
+    }
+}
+```
+
+```java
+// Time spend: 01:37
+class Solution {
+    public List<String> generateParenthesis(int n) {
+        List<String> res = new ArrayList<>();
+        generateParenthesis(res, 0, 0, n, "");
+        return res;
+    }
+
+    public void generateParenthesis(List<String> res, int l, int r, int n, String curr) {
+        if (curr.length() == n * 2) {
+            res.add(curr);
+            return;
+        }
+
+        if (l < n) {
+            generateParenthesis(res, l + 1, r, n, curr + '(');
+        }
+
+        if (r < l) {
+            generateParenthesis(res, l, r + 1, n, curr + ')');
+        }
+    }
+}
+```
+
+```java
+// Time spend: 01:26
+class Solution {
+    public List<String> generateParenthesis(int n) {
+        List<String> res = new ArrayList<>();
+        generateParenthesis(res, 0, 0, n, "");
+        return res;
+    }
+
+    public void generateParenthesis(List<String> res, int l, int r, int n, String curr) {
+        if (curr.length() == n * 2) {
+            res.add(curr);
+            return;
+        }
+
+        if (l < n) {
+            generateParenthesis(res, l + 1, r, n, curr + '(');
+        }
+
+        if (r < l) {
+            generateParenthesis(res, l, r + 1, n, curr + ')');
+        }
+    }
+}
+```