二分查找

package demo3;

public class BinarySearch {

    public String binarySearch(int[] array,int key)
    {
        int left = 0;
        int right = array.length-1;

        while (left<right)
        {
            int mid = left +(right-left)/2;

            if(array[mid]<key)
            {
                left=mid+1;
            }
            else if(array[mid]>key)
            {
                right=right-1;
            }
            else if(array[mid]==key)
            {
                return "yes";
            }

        }


        return "no";

    }
}

package demo3;

public class TestBinarySearch {
    public static void main(String[] args) {
        int[] array = {2,1,1,2,3,5,6,7,21,12};

        BinarySearch binary = new BinarySearch();

        System.out.println(  binary.binarySearch(array,4));
    }


}