How does random shuffling in quick sort help in increasing the efficiency of the code?

Question

I was going through lecture videos by Robert Sedgwick on algorithms, and he explains that random shuffling ensures we don\'t get to encounter the worst case quadratic time s

Answer 1

Is the video in coursera? Unfortunately, shuffle decrease performance to O(N^2) with data n,n,...,n,1,1,...,1. I have inspected Quick.java with nn11.awk that generate such data.

$ for N in 10000 20000 30000 40000; do time ./nn11.awk $N | java Quick; done | awk 'NF>1'

real    0m10.732s
user    0m10.295s
sys     0m0.948s

real    0m48.057s
user    0m44.968s
sys     0m3.193s

real    1m52.109s
user    1m48.158s
sys     0m3.634s

real    3m38.336s
user    3m31.475s
sys     0m6.253s