|0020|Valid Parentheses|[Go]({{< relref "/ChapterFour/0001~0099/0020.Valid-Parentheses.md" >}})|Easy| O(log n)| O(1)||40.6%|

|0032|Longest Valid Parentheses|[Go]({{< relref "/ChapterFour/0001~0099/0032.Longest-Valid-Parentheses.md" >}})|Hard||||31.1%|

|0042|Trapping Rain Water|[Go]({{< relref "/ChapterFour/0001~0099/0042.Trapping-Rain-Water.md" >}})|Hard| O(n)| O(1)|❤️|55.9%|

|0071|Simplify Path|[Go]({{< relref "/ChapterFour/0001~0099/0071.Simplify-Path.md" >}})|Medium| O(n)| O(n)|❤️|37.5%|

|0084|Largest Rectangle in Histogram|[Go]({{< relref "/ChapterFour/0001~0099/0084.Largest-Rectangle-in-Histogram.md" >}})|Hard| O(n)| O(n)|❤️|40.5%|

|0094|Binary Tree Inorder Traversal|[Go]({{< relref "/ChapterFour/0001~0099/0094.Binary-Tree-Inorder-Traversal.md" >}})|Easy| O(n)| O(1)||70.2%|

|0114|Flatten Binary Tree to Linked List|[Go]({{< relref "/ChapterFour/0100~0199/0114.Flatten-Binary-Tree-to-Linked-List.md" >}})|Medium||||57.2%|

|0143|Reorder List|[Go]({{< relref "/ChapterFour/0100~0199/0143.Reorder-List.md" >}})|Medium||||47.0%|

|0144|Binary Tree Preorder Traversal|[Go]({{< relref "/ChapterFour/0100~0199/0144.Binary-Tree-Preorder-Traversal.md" >}})|Easy| O(n)| O(1)||61.9%|

|0145|Binary Tree Postorder Traversal|[Go]({{< relref "/ChapterFour/0100~0199/0145.Binary-Tree-Postorder-Traversal.md" >}})|Easy| O(n)| O(1)||63.3%|

|0150|Evaluate Reverse Polish Notation|[Go]({{< relref "/ChapterFour/0100~0199/0150.Evaluate-Reverse-Polish-Notation.md" >}})|Medium| O(n)| O(1)||41.8%|

|0155|Min Stack|[Go]({{< relref "/ChapterFour/0100~0199/0155.Min-Stack.md" >}})|Easy| O(n)| O(n)||49.7%|

|0173|Binary Search Tree Iterator|[Go]({{< relref "/ChapterFour/0100~0199/0173.Binary-Search-Tree-Iterator.md" >}})|Medium| O(n)| O(1)||65.1%|

|0224|Basic Calculator|[Go]({{< relref "/ChapterFour/0200~0299/0224.Basic-Calculator.md" >}})|Hard| O(n)| O(n)||40.2%|

|0225|Implement Stack using Queues|[Go]({{< relref "/ChapterFour/0200~0299/0225.Implement-Stack-using-Queues.md" >}})|Easy| O(n)| O(n)||52.0%|

|0227|Basic Calculator II|[Go]({{< relref "/ChapterFour/0200~0299/0227.Basic-Calculator-II.md" >}})|Medium||||41.3%|

|0232|Implement Queue using Stacks|[Go]({{< relref "/ChapterFour/0200~0299/0232.Implement-Queue-using-Stacks.md" >}})|Easy| O(n)| O(n)||57.2%|

|0234|Palindrome Linked List|[Go]({{< relref "/ChapterFour/0200~0299/0234.Palindrome-Linked-List.md" >}})|Easy||||46.0%|

|0331|Verify Preorder Serialization of a Binary Tree|[Go]({{< relref "/ChapterFour/0300~0399/0331.Verify-Preorder-Serialization-of-a-Binary-Tree.md" >}})|Medium| O(n)| O(1)||43.6%|

|0341|Flatten Nested List Iterator|[Go]({{< relref "/ChapterFour/0300~0399/0341.Flatten-Nested-List-Iterator.md" >}})|Medium||||58.3%|

|0385|Mini Parser|[Go]({{< relref "/ChapterFour/0300~0399/0385.Mini-Parser.md" >}})|Medium||||35.7%|

|0394|Decode String|[Go]({{< relref "/ChapterFour/0300~0399/0394.Decode-String.md" >}})|Medium| O(n)| O(n)||56.0%|

|0445|Add Two Numbers II|[Go]({{< relref "/ChapterFour/0400~0499/0445.Add-Two-Numbers-II.md" >}})|Medium||||58.3%|

|0496|Next Greater Element I|[Go]({{< relref "/ChapterFour/0400~0499/0496.Next-Greater-Element-I.md" >}})|Easy| O(n)| O(n)||69.6%|

|0503|Next Greater Element II|[Go]({{< relref "/ChapterFour/0500~0599/0503.Next-Greater-Element-II.md" >}})|Medium| O(n)| O(n)||61.7%|

|0581|Shortest Unsorted Continuous Subarray|[Go]({{< relref "/ChapterFour/0500~0599/0581.Shortest-Unsorted-Continuous-Subarray.md" >}})|Medium||||34.0%|

|0589|N-ary Tree Preorder Traversal|[Go]({{< relref "/ChapterFour/0500~0599/0589.N-ary-Tree-Preorder-Traversal.md" >}})|Easy||||75.8%|

|0636|Exclusive Time of Functions|[Go]({{< relref "/ChapterFour/0600~0699/0636.Exclusive-Time-of-Functions.md" >}})|Medium| O(n)| O(n)||59.7%|

|0682|Baseball Game|[Go]({{< relref "/ChapterFour/0600~0699/0682.Baseball-Game.md" >}})|Easy| O(n)| O(n)||69.3%|

|0739|Daily Temperatures|[Go]({{< relref "/ChapterFour/0700~0799/0739.Daily-Temperatures.md" >}})|Medium| O(n)| O(n) ||66.9%|

|0844|Backspace String Compare|[Go]({{< relref "/ChapterFour/0800~0899/0844.Backspace-String-Compare.md" >}})|Easy| O(n)| O(n) ||47.4%|

|0853|Car Fleet|[Go]({{< relref "/ChapterFour/0800~0899/0853.Car-Fleet.md" >}})|Medium||||47.8%|

|0895|Maximum Frequency Stack|[Go]({{< relref "/ChapterFour/0800~0899/0895.Maximum-Frequency-Stack.md" >}})|Hard| O(n)| O(n) ||64.8%|

|0897|Increasing Order Search Tree|[Go]({{< relref "/ChapterFour/0800~0899/0897.Increasing-Order-Search-Tree.md" >}})|Easy||||76.0%|

|0901|Online Stock Span|[Go]({{< relref "/ChapterFour/0900~0999/0901.Online-Stock-Span.md" >}})|Medium| O(n)| O(n) ||62.9%|

|0907|Sum of Subarray Minimums|[Go]({{< relref "/ChapterFour/0900~0999/0907.Sum-of-Subarray-Minimums.md" >}})|Medium| O(n)| O(n)|❤️|33.7%|

|0921|Minimum Add to Make Parentheses Valid|[Go]({{< relref "/ChapterFour/0900~0999/0921.Minimum-Add-to-Make-Parentheses-Valid.md" >}})|Medium| O(n)| O(n)||77.3%|

|0946|Validate Stack Sequences|[Go]({{< relref "/ChapterFour/0900~0999/0946.Validate-Stack-Sequences.md" >}})|Medium| O(n)| O(n)||65.3%|

|1003|Check If Word Is Valid After Substitutions|[Go]({{< relref "/ChapterFour/1000~1099/1003.Check-If-Word-Is-Valid-After-Substitutions.md" >}})|Medium| O(n)| O(1)||57.7%|

|1006|Clumsy Factorial|[Go]({{< relref "/ChapterFour/1000~1099/1006.Clumsy-Factorial.md" >}})|Medium||||54.5%|

|1019|Next Greater Node In Linked List|[Go]({{< relref "/ChapterFour/1000~1099/1019.Next-Greater-Node-In-Linked-List.md" >}})|Medium| O(n)| O(1)||59.5%|

|1021|Remove Outermost Parentheses|[Go]({{< relref "/ChapterFour/1000~1099/1021.Remove-Outermost-Parentheses.md" >}})|Easy| O(n)| O(1)||79.7%|

|1047|Remove All Adjacent Duplicates In String|[Go]({{< relref "/ChapterFour/1000~1099/1047.Remove-All-Adjacent-Duplicates-In-String.md" >}})|Easy| O(n)| O(1)||71.0%|

|1111|Maximum Nesting Depth of Two Valid Parentheses Strings|[Go]({{< relref "/ChapterFour/1100~1199/1111.Maximum-Nesting-Depth-of-Two-Valid-Parentheses-Strings.md" >}})|Medium||||72.8%|

|1190|Reverse Substrings Between Each Pair of Parentheses|[Go]({{< relref "/ChapterFour/1100~1199/1190.Reverse-Substrings-Between-Each-Pair-of-Parentheses.md" >}})|Medium||||65.6%|

|1209|Remove All Adjacent Duplicates in String II|[Go]({{< relref "/ChapterFour/1200~1299/1209.Remove-All-Adjacent-Duplicates-in-String-II.md" >}})|Medium||||56.0%|

|1249|Minimum Remove to Make Valid Parentheses|[Go]({{< relref "/ChapterFour/1200~1299/1249.Minimum-Remove-to-Make-Valid-Parentheses.md" >}})|Medium||||65.2%|

|1653|Minimum Deletions to Make String Balanced|[Go]({{< relref "/ChapterFour/1600~1699/1653.Minimum-Deletions-to-Make-String-Balanced.md" >}})|Medium||||55.3%|

|1673|Find the Most Competitive Subsequence|[Go]({{< relref "/ChapterFour/1600~1699/1673.Find-the-Most-Competitive-Subsequence.md" >}})|Medium||||48.1%|

|1700|Number of Students Unable to Eat Lunch|[Go]({{< relref "/ChapterFour/1700~1799/1700.Number-of-Students-Unable-to-Eat-Lunch.md" >}})|Easy||||67.9%|