记录贴，互勉

669. Trim a Binary Search Tree
Basic idea: if the root < low, all the value of left subtree < low, we want to check the right subtree
if the root > high, all the value of right subtree > high, we need to trim the left subtree

1325. Delete Leaves With a Given Value
We want bottom-top, so we need to put the check condition at the end

112. Path Sum
Every time iterates through a child node, pass the path sum - root.val to the child as targetSum,
the condition is true when the targetSum == child.val

113. Path Sum II
Recursive solution: remove the last element added to the list before returning back.
Problem: when the list is the solution, we need to creat a new ArrayList as ls instead of directly using ls as solution, or it will change the list in our solution list.

437. Path Sum III
Use map to map down how many times the pre-sum we have

129. Sum Root to Leaf Numbers
DFS recursive solution

257. Binary Tree Paths
DFS

236. Lowest Common Ancestor of a Binary Tree
Find the common root that left and right are not null.

lishuzheng1012 发表于 2023-8-15 19:16
中序遍历只写出递归的方法，应该是不会被面试官轻易放过的。很可能让你写迭代的方法，两种都熟练面试官就很 ...

o(N logN) 把，遍历每个结点的时候找下一个都需要遍历left tree。