Binary-Tree

LeetCode 103 note: a normal level-order traversal with every odd level reversed gives the zigzag

LeetCode 1379 note: walk both trees in lockstep; when the original reaches target, the clone’s node at the same position is the answer, comparing node identity

LeetCode 337 note: tree DP where each node returns the best (rob it, skip it) pair; not robbing alternate levels

LeetCode 98 note: every node has a valid range (low, high); going left the upper bound becomes the node and going right the lower bound does; comparing parent and child is not enough

LeetCode 230 note: a BST’s in-order traversal is ascending, so stop an iterative in-order walk at the k-th node

LeetCode 199 note: in a level-order traversal, each level’s rightmost node is what you see from the right

LeetCode 1448 note: pass the path maximum down during DFS; a node is good when its value is at least that maximum

LeetCode 102 note: BFS one whole level at a time, building the next level from the current one; an empty tree returns an empty list

LeetCode 1022 note: on the way down double the current number and add the node’s bit, adding it to the total at a leaf

LeetCode 993 note: cousins share a depth but not a parent; record x’s and y’s depth and parent during DFS and compare

LeetCode 965 note: every value must equal the root’s; compare values while recursing, not the booleans the recursion returns

LeetCode 938 note: prune with the BST order, going only right below low and only left above high, adding nodes inside the range