Why is Quicksort's time complexity O(n log n)?

Quicksort's time complexity is O(n log n) because it divides the input array into smaller subarrays and recursively sorts them. The partitioning step takes O(n) time, and on average, the algorithm splits the array into two equal parts. This results in a logarithmic number of levels in the recursion tree, leading to a time complexity of O(n log n).