Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 9 | Sorting and Searching
9.5 Given a sorted array of strings which is interspersed with empty strings, write a method
to find the location of a given string.
Example: find “ball” in [“at”, “”, “”, “”, “ball”, “”, “”, “car”, “”, “”, “dad”, “”, “”] will return 4
Example: find “ballcar” in [“at”, “”, “”, “”, “”, “ball”, “car”, “”, “”, “dad”, “”, “”] will return -1
SOLUTION
pg 66
Use ordinary binary search, but when you hit an empty string, advance to the next nonempty
string; if there is no next non-empty string, search the left half.
1 public int search(String[] strings, String str, int first, int last) {
2 while (first 1;
11 while (strings[mid] == “”) {
12 ++mid; // will always find one
13 }
14 int r = strings[mid].compareTo(str);
15 if (r == 0) return mid;
16 if (r < 0) {
17 first = mid + 1;
18 } else {
19 last = mid - 1;
20 }
21 }
22 return -1;
23 }
24
25 public int search(String[] strings, String str) {
26 if (strings == null || str == null) return -1;
27 if (str == “”) {
28 for (int i = 0; i < strings.length; i++) {
29 if (strings[i] == “”) return i;
30 }
31 return -1;
32 }
33 return search(strings, str, 0, strings.length - 1);
34 }
1 8 3
Cracking the Coding Interview | Concepts and Algorithms