劍指Offer(牛客網)-數字在排序數組中出現的次數

題目來源：

https://www.nowcoder.com/practice/70610bf967994b22bb1c26f9ae901fa2?tpId=13&tqId=11190&tPage=2&rp=2&ru=%2Fta%2Fcoding-interviews&qru=%2Fta%2Fcoding-interviews%2Fquestion-ranking

題目描述：

統計一個數字在排序數組中出現的次數。

代碼如下：

public class Solution {
    public int GetNumberOfK(int[] array, int k) {
        if (array.length == 0) {
            return 0;
        }
        int firstIndex = getFirstIndex(array, k);
        int lastIndex = getLastIndex(array, k);
        return lastIndex - firstIndex + 1;
    }
    private int getFirstIndex(int[] array, int k) {
        int start = 0, end = array.length - 1;
        int mid = (start + end) / 2;
        while (start <= end) {
            if (array[mid] < k) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
            mid = (start + end) / 2;
        }
        return start;
    }
    private int getLastIndex(int[] array, int k) {
        int start = 0, end = array.length - 1;
        int mid = (start + end) / 2;
        while (start <= end) {
            if (array[mid] <= k) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
            mid = (start + end) / 2;
        }
        return end;
    }
}