Easy

LeetCode 2441 note: keep positives and absolute values of negatives in separate sets and take the largest common value; absolute values alone mistake same-sign duplicates for pairs

LeetCode 3637 note: walk one index through uphill, downhill and uphill; all three runs must be non-empty and reach the end exactly

LeetCode Problem Solving

LeetCode 2210 note: treat equal neighbors as one point and remember only the last non-flat direction; up then down is a hill, down then up a valley

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

LeetCode 3423 note: circular adjacency includes the last and first elements; starting from i = 0 with nums[i - 1] covers it

LeetCode 1290 note: walk head to tail, shifting the running value left by one and adding the new bit

LeetCode 3606 note: filter valid coupons, then sort by (category order, code); character ranges must include z, Z and 9

LeetCode 3550 note: check indices in increasing order, computing each digit sum; the first match is the answer

LeetCode 1979 note: find the minimum and maximum, then take their GCD with Euclid’s algorithm

LeetCode 2094 note: enumerate the even numbers 100 to 998 instead and check that each digit needed is available; Counter subtraction keeps only positives