Simulation

LeetCode 4097 note: only merge the fixed pairs (0,1), (2,3), …, stepping by 2, not every adjacent pair

Simulation by building a list, parsing by trying every pattern at each position, all substrings of length k, counting by character class, checking balanced substrings from a fixed start, and splitting into words

Transposing and rotating, converting between 2D indices and a 1D sequence, neighbors and diagonals, and spiral traversal with four boundaries

Adjacent comparisons and walking monotonic runs (uphill, downhill, hills and valleys), keeping prefix / suffix maximums and sums in one pass, enumerating pairs in small ranges, and breaking ties with tuple keys

Parsing nested structures, simulations that interact with the previous element, monotonic stacks, greedy deletion for the smallest string, and a lazy-deletion Max Stack

LeetCode 2751 note: sort by position, push right-moving robots, and let each left-moving robot collide until one side is gone

LeetCode 3959 note: accumulate the square sum minus the digit sum; each digit adds d² − d ≥ 0, so the gap never shrinks and you can return as soon as it reaches 50

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

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 3819 note: pull out the non-negative values, rotate them left by k, and put them back into the non-negative positions in order; with none, do not take a modulo by 0