Medium

LeetCode 48 note: rotating 90 degrees clockwise is a transpose followed by reversing each row, both in place

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 131 note: each level cuts a palindrome from the front of the remaining string, trying every length from 1 to the whole remainder

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 973 note: as in Top-K, keep a size-k max-heap (negated distances) holding the k closest points

LeetCode 287 note: treat i -> nums[i] as a linked list; the duplicate is the cycle entry, found with Floyd’s algorithm in O(1) space without modifying the array

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

LeetCode 215 note: keep a min-heap of size k whose top is the k-th largest, or use quickselect for O(n) on average

LeetCode 208 note: each node is a children dict plus an is_end flag; insert, search and startsWith all walk down character by character

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