Math

LeetCode 2235 note: return the sum; the C++ version once failed to compile from a missing semicolon

LeetCode 3697 note: each non-zero digit times its place value is one component; output them from the highest place down

LeetCode 3649 note: simplify the condition to “larger absolute value <= 2 × smaller absolute value”, then count with two pointers over sorted absolute values

LeetCode 3648 note: each sensor covers a (2k + 1) × (2k + 1) square, so take a ceiling division in each direction and multiply

Solving the Reverse Polish Notation evaluation problem using stack-based approach

Remainder pairing with a hash map; handle 0 and k/2 remainders carefully.

LeetCode Problem Solving

LeetCode 2709 note: every pair of indices connects ⇔ one component; factor with SPF and union each number with its prime factors in Union-Find, treating 1 specially

LeetCode 3627 note: after sorting, each group takes the two largest and the smallest, with the second largest as the median; the answer takes every other value from the end, n / 3 of them

LeetCode 2745 note: AA and BB must alternate, using min(x, y) pairs plus one extra of the more common kind, and every AB fits in

LeetCode 1304 note: place 1..n/2 and their negatives so each pair cancels, adding 0 when n is odd

LeetCode 3622 note: compute the digit sum and product and test n % (sum + product) == 0, keeping the modulo the right way around