寻找边界值，二分模板，简洁凝练

二分模板

class Solution {
    public static void main(String[] args) {
        int[] arr={1,2,2,2,2,4,5,6};
        int l=0,r=arr.length-1;
        while(l<r){
            int mid=l+(r-l)/2;
            if(arr[mid]>=2) r=mid;
            else l=mid+1;
        }
        System.out.println("l:"+l+"r:"+r);
        System.out.println("left: "+l);
        l=0;r=arr.length-1;
        while(l<r){
            int mid=l+(r-l+1)/2;
            if(arr[mid]<=2) l=mid;
            else r=mid-1;
        }
        System.out.println("l:"+l+"r:"+r);
        System.out.println("right: "+r);

    }
}