二分查找

import java.util.Arrays;

public class SJJG {
   public static void main(String [] args){

       // 二分查找的前提是，数据集有序
       int[] a = {1,3,5,6,7,9,10,11,13,14,16,19,20,107};
       System.out.println(binarySearch(a, 14));
       System.out.println(Arrays.binarySearch(a, 14));// 返回元素索引
   }
   public static int binarySearch(int [] num , int des){
        int start = 0;
        int end = num.length -1;
        while(start <= end){
            int mid = (start + end) / 2 ;
            if(num[mid] == des){
               return num[mid];
            }else if(num[mid] < des){
                start = mid + 1;
            }else if(num[mid] > des){
                end = mid -1;
            }
        }
        return -1;
   }
}