Graded A+ UPDATE 2025|2026!! STUDY GUIDE EXAM
Analyzing runtime
Insert element into position 0 of an array of size n (in java) - (ANSWER)Runs in linear time, (if the array is
size n and you double it, time will be doubles as well, this is a good way to think about linear time).
Analyzing runtime
Retrieving an element from an array of size n (at a particular index, in java). - (ANSWER)When the CPU
has to do the arithmetic to get the element from the specified index, it's a constant time operation. The
arithmetic barley takes any time regardless of what index it is asking for.
(note: the size of arrays in java are bounded to 2^32)
Analyzing runtime
Program that prints all of the n-digit numbers - (ANSWER)It is an exponential function multiplied by a
linear function.
Think about 2 parabolas where one is shallow and the other is steep.
Can we make the shallow one worse than the steep one by multiplying it by a large constant? -
(ANSWER)- Yes, all parabolas are in the same "ballpark."
- It doesn't matter if one parabola starts better by the other, if you multiply it by a big enough number, it
is the same thing.
Imagine a parabola and a shallow line where the line is clearly faster, what if we start multiplying it? will
the line still be better? - (ANSWER)- Multiplying does slow it down but even when we multiply by a large
number, after the crossover we still see that the red line is faster.
- As n goes to infinity, there is no way u can multiply the line by a number and make it worse.
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Graded A+ UPDATE 2025|2026!! STUDY GUIDE EXAM
- Conclusion: lines are better/faster than parabolas.
f(n) as O(g(n)) means: - (ANSWER)As n goes toward infinity, f is either better, (faster/smaller) than g, or
"in the same ballpark."
What does "In the same ballpark" mean? - (ANSWER)- Even though g might seem better (smaller), we
can multiply it by a big number and make it worse (bigger) than f(for big values of n).
- We can find a big enough value m, so that f(n) < mg(n) for sufficiently large n.
On a test Fawzi may ask: show 3n^2 + 15n + 20 is O(n^2)
How would you show that? - (ANSWER)- Determine what number to multiply by n^2 to show that it can
be worse than the first function.
- answer: "I choose the multiplier n = 4, now 3n^2 + 15n + 20 < m(n^2) as long as n > 20.
Show 100n + 150 is O(n) - (ANSWER)- Keep plugging numbers into n until you could prove the answer is
true.
- I choose m = 101
- Now 100n + 150 < m(n) as long as n > 1000
What is the big O of the binary search algorithm? - (ANSWER)O(log n)
If f is linear and g is quadratic, - (ANSWER)then f is O(g) but g is NOT O(f)
If f is linear and g is logarithmic, - (ANSWER)then f is NOT O(g) but g IS O(f)
if f(n) = 2^n and g(n) = 3^n, - (ANSWER)then f is O(g) but g is not O(f)
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Graded A+ UPDATE 2025|2026!! STUDY GUIDE EXAM
f is O(g) meaning - (ANSWER)- f is either better (smaller) than g or at least not dramatically worse.
- this is big O notation
f is o(g) meaning - (ANSWER)f is dramatically better (smaller) than g.
Suppose we have two functions, f(n) and g(n), and we want to know: Are they "in the same ballpark"? if
not, which one is better/worse?
evaluate this limit:
lim (f(n)/g(n))
n --> infinity
What does it mean if this limit comes out as 0? - (ANSWER)If this limit comes out as zero that means
whatever is in the denominator is getting bigger dramatically faster than whatever is on top, so f is faster.
We can write this in little o notation:
f(n) is o(g(n))
Suppose we have two functions, f(n) and g(n), and we want to know: Are they "in the same ballpark"? if
not, which one is better/worse?
evaluate this limit:
lim (f(n)/g(n))
n --> infinity
What does it mean if this limit diverges? (goes to infinity) - (ANSWER)If the limit diverges (goes to
infinity) f is growing much faster so in little o notation we would write:
g(n) is o(f(n))
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Graded A+ UPDATE 2025|2026!! STUDY GUIDE EXAM
Suppose we have two functions, f(n) and g(n), and we want to know: Are they "in the same ballpark"? if
not, which one is better/worse?
evaluate this limit:
lim (f(n)/g(n))
n --> infinity
What does it mean if this limit equals a non zero constant? - (ANSWER)f(n) is theta(g(n))
(check lecture 40 for theta notation)
Analyzing code fragments
for (int i= 0; i< n; i++) {
System.out.println("Hi");
} - (ANSWER)O(n)
Analyzing code fragments
for (int i= 0; i< 100 * n; i++) {
System.out.println("HI");
} - (ANSWER)O(n)
Analyzing code fragments
for (int i= 0; i< n; i++) {