Solve T(n)=2T(n/2)+n — connect to merge sort analysis.

Master theorem sketch

For T(n)=2T(n/2)+n (merge sort), divide into halves at log n levels, n work per level → O(n log n).

// T(n) = aT(n/b) + f(n)
// a=2, b=2, f(n)=n → O(n log n)