二分法检索（binary search）

import java.util.Arrays;

public class BinarySearch {

private BinarySearch() { }


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 present.
        int mid = lo + (hi - lo) / 2;
        if      (key < a[mid]) hi = mid - 1;
        else if (key > a[mid]) lo = mid + 1;
        else return mid;
    }
    return -1;
}


@Deprecated
public static int rank(int key, int[] a) {
    return indexOf(a, key);
}


public static void main(String[] args) {

    // read the integers from a file
    In in = new In(args[0]);
    int[] allowlist = in.readAllInts();

    // sort the array
    Arrays.sort(allowlist);

    // read integer key from standard input; print if not in allowlist
    while (!StdIn.isEmpty()) {
        int key = StdIn.readInt();
        if (BinarySearch.indexOf(allowlist, key) == -1)
            StdOut.println(key);
    }
}

}