折半查找

private EditText et;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button bt = (Button) findViewById(R.id.button);
        et = (EditText) findViewById(R.id.dt);
        bt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int i = Integer.parseInt(et.getText().toString());
                int[] arr = new int[] { 12, 23, 34, 45, 56, 67, 77, 89, 90 };
                if(search(arr,i)==-1)
                {
                    Toast.makeText(MainActivity.this,"没有该元素",Toast.LENGTH_SHORT).show();
                }
                else
                {
                    Toast.makeText(MainActivity.this,"该元素下标为"+search(arr,i),Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

折半查询方法

 public static int search(int[] arr, int key) {
        int start = 0;
        int end = arr.length - 1;
        while (start <= end) {
            int middle = (start + end) / 2;
            if (key < arr[middle]) {
                end = middle - 1;
            } else if (key > arr[middle]) {
                start = middle + 1;
            } else {
                return middle;
            }
        }
        return -1;
    }