page61-将二分查找重写为一段面向对象的程序

import java.util.Arrays;

public class StaticSETofInts {
    
    private int[] a;
    public StaticSETofInts(int[] keys){
        
        a = new int[keys.length];
        for (int i = 0; i < keys.length; i++) 
            a[i] = keys[i];//保护性复制
        Arrays.sort(a);
    }

    public boolean contains(int key){
        return  rank(key) != -1;
    }
    
    private int rank(int key){//二分查找
        
        int low = 0;
        int high = a.length -1;
        while(low <= high){ //要么存在于a[low..high]中， 要么不存在。
            
            int mid = (low + high) /2;
            if(key < a[mid]) high = mid -1;
            else if(key > a[mid]) low  = mid + 1;
            else return mid;
        }
        return -1;
    }
}

public class Whitelist {
    
    public static void main(String[] args) {
        
        int[] w = new In(args[0]).readAllInts();
        StaticSETofInts set = new StaticSETofInts(w);
        
        while(!StdIn.isEmpty()){
            int key = StdIn.readInt();
            if(!set.contains(key)) System.out.println(key);
        }
    }
}