算法-二分查找算法

package sort;

public class TwoFenSearch {

    public static void main(String[] args) {
        int[] arr = {1,2,3,4,5,6,7,8,11,15,17};
        int i1 = binarySearch(arr, 11);
        System.out.println(i1);
        int i2 = binarySearch(arr, 17,0,arr.length-1);
        System.out.println(i2);
    }

    /**
     * 循環查找
     */
    public static int binarySearch(int[] arr,int num){
        int low = 0;
        int high =arr.length-1;
        while(low<=high){
            int middle = (low+high)/2;
            if(num==arr[middle]){
                return middle;
            }else if(num>arr[middle]){
                low=middle+1;
            }else {
                high=middle-1;
            }
        }
        return -1;

    }

    /**
     * 遞歸查找
     */
    public static int binarySearch(int[] arr,int num,int low,int high){
        int middle = (low+high)/2;
        if(num<arr[low]||num>arr[high]||low>high){
            return -1;
        }
        if(num<arr[middle]){
           return  binarySearch(arr,num,low,middle-1);
        }else if(num>arr[middle]){
            return  binarySearch(arr,num,middle+1,high);
        }else
            return middle;
    }

}