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BinarySearch.java
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73 lines (67 loc) · 1.91 KB
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import java.util.Arrays;
/**
* The class provides a static method for binary searching for an integer in a sorted array of integers.
* The `indexOf` operations takes logarithmic time in the worst case.
*
*/
public class BinarySearch {
private BinarySearch {}
/**
* Returns the index of the specified key in the specified array.
*
* @param a: the array if integers, must be sorted in ascending order
* @param key: the search key
* @return the index of key in array if present, -1 otherwise
*
*/
public static int indexOf(int[] a, int key) {
int lo = 0;
int hi = a.length - 1;
while(lo <= hi) {
// key is in a[lo, hi] or not exist
int mid = (hi - lo) / 2 + lo;
if(key < a[mid])
hi = mid - 1;
else if(key > a[mid])
lo = mid + 1;
else
return mid;
}
return -1;
}
/**
* Return the index of the specified key in the specified array.
* This function is poorly named because it doesn't give the rank
* if the array has duplicate keys or if the key isn't in the array.
*
* @param key: the search key
* @param a: the array of integers, must be sorted in ascending order
* @return index of key in array if exist, -1 otherwise
*
*/
@Deprecated
public static int rank(int key, int[] a) {
return indexOf(a, key);
}
/**
* Reads in a sequence of integers from the whitelist file, specific as
* a command-line argument; reads in integers from standard input;
* prints to standard output those integers that don't appear in the file.
*
* @param args: the command-line arguments
*
*/
public static void main(String[] args) {
// read the integers from file
In in = new In(args[0])
int[] whitelist = in.readAllInts();
// sort
Arrays.sort(whitelist);
// read integer key from standard input, print if not in whitelist
while(!StdIn.isEmpty()) {
int key = StdIn.readInt();
if(BinarySearch.indexOf(whitelist, key) == -1)
StdOut.println(key);
}
}
}