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摘要： use two stacks 阅读全文

摘要： 带返回值的 recursion Given an array where elements are sorted in ascending order, convert it to a height balanced BST. For this problem, a height-balanced 阅读全文

摘要： TreeNode head = null; TreeNode prev = null; public void inOrder(TreeNode root){ if(root == null) return; inOrder(root.left); if(prev == null){ head = root; }else{ prev.right = root... 阅读全文

摘要： Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST. For this problem, a height-balanced bina 阅读全文

摘要： 把自己写的solution 1 和 闫老师写的solution2 都弄懂，会写。 bst变double linked list。recursion秒了，然后第一个follow up是把双链表变回去，要求balance。第二个follow up是在牺牲空间复杂度的情况下如何优化时间，想了个时间O(n) 阅读全文

摘要： Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers. If such arrangement is not possib 阅读全文

摘要： 301. Remove Invalid Parentheses Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results. Note: The input string may contain letters oth... 阅读全文