Cracking the Coding Interview - Fooo

Solutions to Chapter 10 | Mathematical
Q3 -> append x*3, x*5 and x*7 to Q3, Q5 and Q7. Remove x from Q3.
Q5 -> append x*5 and x*7 to Q5 and Q7. Remove x from Q5.
Q7 -> only append x*7 to Q7. Remove x from Q7.
Note: we do not need to append x*3 and x*5 to all lists because
they will already be found in another list.
6. Repeat steps 4 - 6 until we’ve found k elements.
1 public static int getKthMagicNumber(int k) {
2 if (k 0; --k) { // We’ve done one iteration already.
11 val = Math.min(Q3.peek().intValue(),
12 Math.min(Q5.peek().inValue(), Q7.peek().intValue()));
13 if (val == Q7.peek()) {
14 Q7.remove();
15 } else {
16 if (val == Q5.peek()) {
17 Q5.remove();
18 } else { // must be from Q3
19 Q3.remove();
20 Q3.add(val * 3);
21 }
22 Q5.add(val * 5);
23 }
24 Q7.add(val * 7);
25 }
26 return val;
27 }
OBSERVATIONS AND SUGGESTIONS:
When you get this question, do your best to solve it—even though it’s really difficult Explain
a brute force approach (not as tricky) and then start thinking about how you can optimize it
Or, try to find a pattern in the numbers
Chances are, your interviewer will help you along when you get stuck Whatever you do,
don’t give up! Think out loud, wonder aloud, explain your thought process Your interviewer
will probably jump in to guide you
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