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| 1 | +import java.util.Arrays; |
| 2 | + |
| 3 | +/** |
| 4 | + * The class provides a static method for binary searching for an integer in a sorted array of integers. |
| 5 | + * The `indexOf` operations takes logarithmic time in the worst case. |
| 6 | + * |
| 7 | + */ |
| 8 | +public class BinarySearch { |
| 9 | + private BinarySearch {} |
| 10 | + |
| 11 | + /** |
| 12 | + * Returns the index of the specified key in the specified array. |
| 13 | + * |
| 14 | + * @param a: the array if integers, must be sorted in ascending order |
| 15 | + * @param key: the search key |
| 16 | + * @return the index of key in array if present, -1 otherwise |
| 17 | + * |
| 18 | + */ |
| 19 | + public static int indexOf(int[] a, int key) { |
| 20 | + int lo = 0; |
| 21 | + int hi = a.length - 1; |
| 22 | + while(lo <= hi) { |
| 23 | + // key is in a[lo, hi] or not exist |
| 24 | + int mid = (hi - lo) / 2 + lo; |
| 25 | + if(key < a[mid]) |
| 26 | + hi = mid - 1; |
| 27 | + else if(key > a[mid]) |
| 28 | + lo = mid + 1; |
| 29 | + else |
| 30 | + return mid; |
| 31 | + } |
| 32 | + return -1; |
| 33 | + } |
| 34 | + |
| 35 | + /** |
| 36 | + * Return the index of the specified key in the specified array. |
| 37 | + * This function is poorly named because it doesn't give the rank |
| 38 | + * if the array has duplicate keys or if the key isn't in the array. |
| 39 | + * |
| 40 | + * @param key: the search key |
| 41 | + * @param a: the array of integers, must be sorted in ascending order |
| 42 | + * @return index of key in array if exist, -1 otherwise |
| 43 | + * |
| 44 | + */ |
| 45 | + @Deprecated |
| 46 | + public static int rank(int key, int[] a) { |
| 47 | + return indexOf(a, key); |
| 48 | + } |
| 49 | + |
| 50 | + /** |
| 51 | + * Reads in a sequence of integers from the whitelist file, specific as |
| 52 | + * a command-line argument; reads in integers from standard input; |
| 53 | + * prints to standard output those integers that don't appear in the file. |
| 54 | + * |
| 55 | + * @param args: the command-line arguments |
| 56 | + * |
| 57 | + */ |
| 58 | + public static void main(String[] args) { |
| 59 | + // read the integers from file |
| 60 | + In in = new In(args[0]) |
| 61 | + int[] whitelist = in.readAllInts(); |
| 62 | + |
| 63 | + // sort |
| 64 | + Arrays.sort(whitelist); |
| 65 | + |
| 66 | + // read integer key from standard input, print if not in whitelist |
| 67 | + while(!StdIn.isEmpty()) { |
| 68 | + int key = StdIn.readInt(); |
| 69 | + if(BinarySearch.indexOf(whitelist, key) == -1) |
| 70 | + StdOut.println(key); |
| 71 | + } |
| 72 | + } |
| 73 | +} |
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