1、二分查找

--704

import java.lang.annotation.Target;

public class _704 {
    public static void main(String[] args) {
        _704 test=new _704();
        int[] nums = new int[]{-1,0,3,5,9,12};
        int target = 2;
        System.out.println(test.search(nums, target));
    }
    public int search(int[] nums,int target){
        if(target<nums[0] || target>nums[nums.length-1])
            return -1;
        int low=0,high=nums.length-1;

        while (low<=high){
            int middle=low+((high-low)>>1);
            if(target>nums[middle])
                low=middle+1;
            else if(target<nums[middle])
                  high=middle-1;
            else
                return middle;
        }
        return -1;
    }
}