二分法查找

二分法查找的前提数组是有序的


 1 package test;

public class BinarySearch {
    public static void main(String[] args) {
        int[] arr = new int[] { 12, 23, 34, 45, 56, 67, 77, 89, 90 };
        int key = 89;
        int target = search(arr, key);
        if (target == -1) {
            System.out.println("数组中没有此数");
        } else {
            System.out.println(key + "在数组arr第" + target + "位");
        }

    }

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