二分查找

import java.util.Arrays;
public class BinarySearch
{
public static int rank(int key, int[] a)
{ // 数组必须是有序的
int lo = 0;
int hi = a.length - 1;
while (lo <= hi)
{ // 被查找的键要么不存在，要么必然存在于a[lo..hi] 之中
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;
}
public static void main(String[] args)
{
int[] whitelist = In.readInts(args[0]);
Arrays.sort(whitelist);
while (!StdIn.isEmpty())
{ // 读取键值，如果不存在于白名单中则将其打印
int key = StdIn.readInt();
if (rank(key, whitelist) < 0)
StdOut.println(key);
}
}