Friends Of Appropriate Ages

Translate the rules before optimizing. A person of age A cannot request B when B is at most 0.5A plus 7, when B is greater than A, or under the special age-100 condition from the stated problem. With ages bounded to 120, build frequency counts. For each sender age A, identify the smallest integer B strictly greater than 0.5A plus 7 and the largest B no greater than A; sum counts[B] across that interval, then subtract one for the sender when A itself is in range. Prefix counts make each interval query O(1), or sorted ages support two pointers. Be explicit that requests are directed: if both people qualify, both directions count. Test ages below the threshold, duplicates of one age, age 100 and above, and no valid recipients. With fixed age range, time is O(n+A^2) or O(n+A) with prefix sums, and space is O(A), where A=120; sorting is O(n log n).