二分查找

二分查找

前提：有序
思路：
mid = (left + right) / 2
若 mid = value , 输出 mid 下标
若 mid < value , mid = left + 1
若 mid > value , mid = right - 1

public class Test2 {

    @Test
    public void test1() {
        int[] arr = {-99,-54,-2,0,0,2,33,43,256,999};
        int left = 0;
        int right = arr.length - 1;
        int value = -99;
        //value 对应的索引
        int index = -1;

        while (left <= right) {
            int mid = (left + right) / 2;
            if (value == arr[mid]){
                index = mid;
                break;
            } else if (value < arr[mid]) {
                right = mid - 1;
            }else if (value > arr[mid]) {
                left = mid + 1;
            }
        }

        if (index == -1){
            System.out.println("没有");
        }else {
            System.out.println("索引为：" + index);
        }
    }
}