Array

LeetCode 3835 note: cost = (max - min) × length only grows as the window grows, so a sliding window counts subarrays; two monotonic deques keep the window’s max and min

LeetCode 3834 note: a stack simulation where a new element merges with an equal top, possibly again with the new top

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 244 note: precompute each word’s positions (sorted by construction), then answer each query by merging the two position lists with two pointers, always advancing the smaller one

LeetCode 986 note: two pointers each hold an interval, the intersection is [max(starts), min(ends)], and the interval that ends first cannot meet anything else, so its pointer advances

LeetCode 3828 note: Alice can leave only the first or last element on her first move, guaranteeing max(first, last); Bob can likewise keep only an end, and one deletion changes at most one end, so the answer is max(first, last)

LeetCode 1537 note: two sorted arrays can switch only at shared values; merge with two pointers, keep a running sum per path, and at a shared value set both to the larger sum plus that value

LeetCode 809 note: two pointers compare runs of equal characters; when the lengths differ, the run in s must be at least 3 and no shorter than the word’s run, and both strings must end together

LeetCode 442 note: values are in 1..n, so mark v with the sign of nums[v-1]; on the second visit it is already negative

LeetCode 41 note: the answer is in 1..n+1; replace impossible values with n+1 (not 0) and mark v as seen with the sign of nums[v-1]

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