Stack

• 括号匹配问题及类似问题。第 20 题，第 921 题，第 1021 题。

• 栈的基本 pop 和 push 操作。第 71 题，第 150 题，第 155 题，第 224 题，第 225 题，第 232 题，第 946 题，第 1047 题。

• 利用栈进行编码问题。第 394 题，第 682 题，第 856 题，第 880 题。

• 单调栈。利用栈维护一个单调递增或者递减的下标数组。第 84 题，第 456 题，第 496 题，第 503 题，第 739 题，第 901 题，第 907 题，第 1019 题。

No.	Title	Solution	Difficulty	TimeComplexity	SpaceComplexity	Favorite	Acceptance
0020	Valid Parentheses		Easy	O(log n)	O(1)		39.8%
0042	Trapping Rain Water		Hard	O(n)	O(1)	❤️	50.8%
0071	Simplify Path		Medium	O(n)	O(n)	❤️	33.6%
0084	Largest Rectangle in Histogram		Hard	O(n)	O(n)	❤️	36.9%
0094	Binary Tree Inorder Traversal		Medium	O(n)	O(1)		65.5%
0103	Binary Tree Zigzag Level Order Traversal		Medium	O(n)	O(n)		49.8%
0144	Binary Tree Preorder Traversal		Medium	O(n)	O(1)		57.2%
0145	Binary Tree Postorder Traversal		Medium	O(n)	O(1)		57.2%
0150	Evaluate Reverse Polish Notation		Medium	O(n)	O(1)		37.6%
0155	Min Stack		Easy	O(n)	O(n)		46.1%
0173	Binary Search Tree Iterator		Medium	O(n)	O(1)		59.7%
0224	Basic Calculator		Hard	O(n)	O(n)		38.0%
0225	Implement Stack using Queues		Easy	O(n)	O(n)		47.0%
0232	Implement Queue using Stacks		Easy	O(n)	O(n)		51.7%
0331	Verify Preorder Serialization of a Binary Tree		Medium	O(n)	O(1)		40.9%
0385	Mini Parser		Medium				34.3%
0394	Decode String		Medium	O(n)	O(n)		52.4%
0402	Remove K Digits		Medium	O(n)	O(1)		28.6%
0456	132 Pattern		Medium	O(n)	O(n)		30.6%
0496	Next Greater Element I		Easy	O(n)	O(n)		65.2%
0503	Next Greater Element II		Medium	O(n)	O(n)		58.2%
0636	Exclusive Time of Functions		Medium	O(n)	O(n)		54.0%
0682	Baseball Game		Easy	O(n)	O(n)		66.2%
0726	Number of Atoms		Hard	O(n)	O(n)	❤️	51.0%
0735	Asteroid Collision		Medium	O(n)	O(n)		43.2%
0739	Daily Temperatures		Medium	O(n)	O(n)		64.4%
0844	Backspace String Compare		Easy	O(n)	O(n)		46.8%
0856	Score of Parentheses		Medium	O(n)	O(n)		62.3%
0880	Decoded String at Index		Medium	O(n)	O(n)		28.3%
0895	Maximum Frequency Stack		Hard	O(n)	O(n)		62.2%
0901	Online Stock Span		Medium	O(n)	O(n)		61.2%
0907	Sum of Subarray Minimums		Medium	O(n)	O(n)	❤️	33.2%
0921	Minimum Add to Make Parentheses Valid		Medium	O(n)	O(n)		74.7%
0946	Validate Stack Sequences		Medium	O(n)	O(n)		63.5%
1003	Check If Word Is Valid After Substitutions		Medium	O(n)	O(1)		56.2%
1019	Next Greater Node In Linked List		Medium	O(n)	O(1)		58.2%
1021	Remove Outermost Parentheses		Easy	O(n)	O(1)		78.7%
1047	Remove All Adjacent Duplicates In String		Easy	O(n)	O(1)		70.3%
1673	Find the Most Competitive Subsequence		Medium				45.1%
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