二分查找写法

 牛客网题目：统计一个数字在排序数组中出现的次数。

public class Solution {
    public int GetNumberOfK(int [] array , int k) {
        int length = array.length;
        if(length == 0){
            return 0;
        }
        int firstK = getFirstK(array, k, 0, length-1);
        int lastK = getLastK(array, k, 0, length-1);
        return lastK - firstK + 1;

    }
    //递归写法
    private int getFirstK(int [] array , int k, int start, int end){
      if(start > end){
           return start;
       }
        int mid = (end-start)/2 + start;
        if(array[mid] < k){
            return getFirstK(array, k, mid+1, end);
        }else {
            return getFirstK(array, k, start, mid -1);
        } 
    }

    //循环写法
    private int getLastK(int [] array , int k, int start, int end){
        int length = array.length;
        while(start <= end){
            int mid = (end-start)/2 + start;
            if(array[mid] > k){
                end = mid-1;
            }else if(array[mid] <= k){
                start = mid+1;
            }
        }
        return end;
    }
}

 二分查找的套路链接：https://www.cnblogs.com/luoxn28/p/5767571.html

https://www.zhihu.com/question/36132386/answer/530313852