Lesson 7.1 · Answer it

Count the comparisons

5 marksYou mark it yourself against the marking points

This function counts how many race times in a list are over a limit. Each time is a whole number of seconds.

def count_over(times, limit):
    over = 0
    for t in times:
        if t > limit:
            over = over + 1
    return over

public static int countOver(
        int[] times, int limit) {
    int over = 0;
    for (int t : times) {
        if (t > limit) {
            over = over + 1;
        }
    }
    return over;
}

Count the comparison t > limit as one step.

(a) State how many times the comparison runs for a list of 200 times. [1]

(b) State, in terms of n, how many times the comparison runs for a list of n race times. [1]

(c) On Mei's laptop, a list of 2000 times takes 6 milliseconds. Assume the time grows in step with the number of comparisons. Estimate the time for a list of 20000 times on the same laptop. [1]

(d) The function is run on a list of 2000 times that are all over the limit, and then on a list of 2000 times that are all under it. State how many comparisons each run makes, and explain why. [2]

[5]

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