Depth-First-Search

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 695 note: DFS each unvisited 1 to measure its island and keep the maximum; cells are the integer 1, not a string

LeetCode 417 note: walk inward from each ocean’s shore to cells no lower than the current one; cells reached from both oceans are the answer

LeetCode 133 note: during DFS map each old node to its copy and return the existing copy when revisited, avoiding infinite recursion; an empty graph returns None

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 79 note: backtrack from every cell, matching the next character in four directions with visited cells marked temporarily and restored; prune early with character counts

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