What is the time complexity of following function fun()? Assume that log(x) returns log value in base 2.
void fun() { int i, j; for (i=1; i<=n; i++) for (j=1; j<= log (i); j++) printf ( "GeeksforGeeks" ); } |
Time Complexity of the above function can be written as Θ(log 1) + Θ(log 2) + Θ(log 3) + . . . . + Θ(log n) which is Θ (log n!)
Order of growth of ‘log n!’ and ‘n log n’ is same for large values of n, i.e., Θ (log n!) = Θ(n log n). So time complexity of fun() is Θ(n log n).
The expression Θ(log n!) = Θ(n log n) can be easily derived from following Stirling’s approximation (or Stirling’s formula).
log n! = n log n - n + O(log(n))
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Sources:
http://en.wikipedia.org/wiki/Stirling%27s_approximation
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