Given a binary tree, find the leftmost value in the last row of the tree.

Given the root of a tree, you are asked to find the most frequent subtree sum. The subtree sum of a node is defined as the sum of all the node values formed by the subtree rooted at that node (including the node itself). So what is the most frequent subtree sum value? If there is a tie, return al…

Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST.

其实这道题目不难，只要捋清楚一些边界的场景即可。自上而下遍历数组时，一定是自右往左移动的，因此下标移动的方向为[row, column]=>[row+1, column-1]。自上而下有两种边界场景，一个是到达了左边界，此时的…

Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not.