Activity Selection Problem:

You are given n activities with their start and finish times. Select the maximum number of activities that can be performed by a single person, assuming that a person can only work on a single activity at a time.

Consider the following 6 activities 
sorted by by finish time.
     start[]  =  {1, 3, 0, 5, 8, 5};
     finish[] =  {2, 4, 6, 7, 9, 9};
A person can perform at most four activities. The 
maximum set of activities that can be executed 
is {0, 1, 3, 4} [ These are indexes in start[] and 
finish[] ]

Steps:

1) Sort the activities according to their finishing time
2) Select the first activity from the sorted array and print it.
3) Do following for remaining activities in the sorted array.
…….a) If the start time of this activity is greater than or equal to the finish time of previously selected activity then select this activity and print it.

Following is my Python code:

def activitySelection(start,finish):
    i = 0
    print (i,)

    for j in range(1,len(finish)):
        if start[j] > finish[i]:
            print(j,)
            i = j

start = [1 , 3 , 0 , 5 , 8 , 5]
finish = [2 , 4 , 6 , 7 , 9 , 9]

activitySelection(start, finish)

With Sorted: O(n)

Without Sorted: O(n logn)