1) by substitution = c) O(n^2)
2) by master's theorem case 2 = a) O(n)
3) by master's theorem case 2 = b) O(nlogn)
4) by substitution = b) O(nlogn)
in 4th T(n)= T(0) + log 1 + log 2 + ... + log (n - 1) + log n
T(n)= T(0) + log(1*2*3*...........*n)
T(n)=log(n!)
T(n)=log(n^n)
T(n)=nlog(n)