Easy

LeetCode 3903 note: the first index where the prefix maximum minus the suffix minimum is <= k; build the suffix minimum right to left first

LeetCode 3898 note: the number of ones in row i of the adjacency matrix is vertex i’s degree

LeetCode note for Find if Path Exists in Graph, rebuilt from the original learning note

LeetCode 1826 note: at the first mismatch, test both “who dropped a value” explanations; if both fit, it cannot be determined, so return -1

LeetCode 3884 note: compare from both ends toward the middle; the first match is the answer, and odd lengths always match in the middle

LeetCode 3842 note: toggle membership in a set, or keep bulbs appearing an odd number of times, then sort

LeetCode 3838 note: sum each word’s letter weights mod 26 and map backward: 0 -> z, i.e. chr(ord(‘z’) - r)

LeetCode 3833 note: keep a suffix sum from the right and compare nums[i] × count > sum on the right, with no floats and without counting itself

LeetCode 3379 note: moving nums[i] steps right or left is nums[(i + nums[i]) % n]; Python’s % returns a non-negative result for negatives too

LeetCode 3827 note: the only numbers with all-equal bits are 0 and 2^k - 1, so the count is (n + 1).bit_length()

LeetCode 3823 note: two converging-pointer passes, swapping only letters the first time and only special characters the second

LeetCode 2570 note: merge two id-sorted arrays with two pointers, adding values when ids match