记录贴，互勉

508. Most Frequent Subtree Sum
map down the most frequency and the sum happended

124. Binary Tree Maximum Path Sum
For the left and right subPath, we need to compare the value with 0, if it less than 0, we don't add it up

543. Diameter of Binary Tree
Diameter means the maximum length of left and right subTree of a root.

687. Longest Univalue Path
We need to pass the root value of the current path to next layer, and check if cur root value equal its parent root value.

968. Binary Tree Cameras
Hard (DFS)
Hint: need to check the root status at the end.
Define the status of each node:
status = 0,1,2 need a camera, don't need, the camera itself

337. House Robber III
Medium
经典题目: take or not take
For the current root node, we can either take or not take, we use a recursive function to calculate the maximum value we can get, we start from the bottom to the top, if we take current node, the child couldn't be take, but the grandchild could be either take or not take.
In this question, we need to use memory to prevent multiple calculations.
As the bottom node already calculated once for its best result, we just need to check whether we take the root value or not take but the maximum value of its left and right child.

979. Distribute Coins in Binary Tree
Medium
For this question, we can think about the question as a root and left right subtree, for each subTree, the coin it need is abs of( sum of add node - number of node (each node need one) ) (Total move needed)  for the root node, the coin we need to give out is, sum of left and right + root.val -1

目前为止完成部分Tree相关题目

169. Majority Element
Easy

153. Find Minimum in Rotated Sorted Array Medium
Compare mid and end values in the array return the min value if the array left have only one or two value.