2021刷题打卡

6/14/21

1588. Sum of All Odd Length Subarrays, Time: O(), Space: O()
557. Reverse Words in a String III, Time: O(N), Space: O(N)
1323. Maximum 69 Number, Time: O(N), Space: O(N)
876. Middle of the Linked List, Two pointers, Time: O(N), Space: O(1)
21. Merge Two Sorted Lists, Time: O(N), Space: O(1)
206. Reverse Linked List, Time: O(N), Space: O(1)
237. Delete Node in a Linked List, Time: O(1), Space: O(1)

6/15/21

1351. Count Negative Numbers in a Sorted Matrix, Time: O(M * N), Space: O(1)
242. Valid Anagram, Time: O(N), Space: O(1)
1748. Sum of Unique Elements, Map, Time: O(N), Space: O(N)

6/16/21

283. Move Zeroes, Time: O(N), Space: O(1)

6/17/21

Tree专题
617. Merge Two Binary Trees, Time: O(N), Space: O(N)
700. Search in a Binary Search Tree, Time: O(N), Space: O(H)
104. Maximum Depth of Binary Tree, DFS / BFS, Time: O(N), Space: O(H)
559. Maximum Depth of N-ary Tree, Time: O(N), Space: O(H)
226. Invert Binary Tree, D&C, Time: O(N), Space: O(H)
94. Binary Tree Inorder Traversal, 递归, 非递归用stack, Time: O(N), Space: O(H)
100. Same Tree, Time: O(N), Space: O(H)
872. Leaf-Similar Trees, 用两个list记录, list1.equals(list2), Time: O(N), Space: O(N)
606. Construct String from Binary Tree, DFS, 用sb记录, 每次先将当前root.val加入sb, 左边直接加并且继续往下搜, 右边检查存在的情况下再加和往下做, 这样就可以避免没用的(), Time: O(N), Space: O(H)
108. Convert Sorted Array to Binary Search Tree, Time: O(N), Space: O(H)

6/18/21

Tree
144. Binary Tree Preorder Traversal, 非递归时, 最后顺序根左右, 所以用stack存的根, pop根的时候再右左, Time: O(N), Space: O(H)
145. Binary Tree Postorder Traversal, Time: O(N), Space: O(H)
637. Average of Levels in Binary Tree, Double和Integer运算结果是Double, Time: O(N), Space: O(N)

6/19/21

Tree
653. Two Sum IV - Input is a BST, Set记录曾经出现过的val, Time: O(N), Space: O(H)
965. Univalued Binary Tree, Time: O(N), Space: O(H)
1022. Sum of Root To Leaf Binary Numbers, Time: O(N), Space: O(H)
589. N-ary Tree Preorder Traversal, Time: O(N), Space: O(H)
590. N-ary Tree Postorder Traversal, Time: O(N), Space: O(H)
897. Increasing Order Search Tree, inorder是升序的, Time: O(N), Space: O(H)
101. Symmetric Tree, Time: O(N), Space: O(H)
404. Sum of Left Leaves, DFS, Time: O(N), Space: O(H)
257. Binary Tree Paths, Time: O(N), Space: O(H)
993. Cousins in Binary Tree, BFS, 只要和层相关的首先想BFS, Time: O(N), Space: O(N)

同求加群！每天刷题8-12道左右，一个月计划刷300道~

6/20/21

Tree
110. Balanced Binary Tree, Time: O(N), Space: O(H)
111. Minimum Depth of Binary Tree, 正常算完left & right的depth, 分别判断一下左右什么情况决定return什么值, Time: O(N), Space: O(H)
543. Diameter of Binary Tree, 每个点的最长path:left + right, Time: O(N), Space: O(H)
563. Binary Tree Tilt, Time: O(N), Space: O(H)
572. Subtree of Another Tree, Time: O(N), Space: O(H)
270. Closest Binary Search Tree Value, Time: O(N), Space: O(H)

6/21/21
199. Binary Tree Right Side View, Time: O(N), Space: O(N)

6/22/21

235. Lowest Common Ancestor of a Binary Search Tree
671. Second Minimum Node In a Binary Tree
783. Minimum Distance Between BST Nodes
530. Minimum Absolute Difference in BST

6/23/21

112. Path Sum
501. Find Mode in Binary Search Tree

6/22/21

235. Lowest Common Ancestor of a Binary Search Tree
671. Second Minimum Node In a Binary Tree
783. Minimum Distance Between BST Nodes
530. Minimum Absolute Difference in BST

6/23/21

112. Path Sum
501. Find Mode in Binary Search Tree