二分法查找 BinarySearch

Posted 2021-03-17 baishiming

查找一个元素的下标
二分查找使用于已经排好序的数组，定义两个变量， 一个low和一个high, 则mid = (low+high)/2;

如果 value == arr[mid]，返回mid;
如果 value > arr[mid] 在高位查找 low = mid +1;
如果 value < arr[mid] 在地位查找 high = mid - 1;

public class BinarySearch {

    public static void main(String[] args) {
        int[] arr= {7, 8, 9, 10, 12, 20, 30, 40, 50, 80, 100};
        System.out.println(binarySearch(arr,50));
    }

    public static int binarySearch (int[] arr,int value){
        int low = 0;
        int heigh = arr.length - 1;
        while (low <= heigh){
            int mid = (low+heigh)/2;
            if(arr[mid] == value){
                return mid;
            }
            if(arr[mid] < value){
                low = mid + 1;
            }
            if(arr[mid] > value){
                heigh = mid - 1;
            }
        }
        return -1;
    }
}