题解 | #数字在升序数组中出现的次数#

public class Solution {
    public int GetNumberOfK(int[] array, int k) {
        //二分法
        if (array == null || array.length < 1) {
            return 0;
        }

        int start = 0;
        int end = array.length - 1;
        int mid = 0;

        //先用二分法找到k点
        while (start <= end) {
            mid = start + (end - start) / 2;
            if (array[mid] == k) {
                break;
            } else if (array[mid] < k) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }

        if (array[mid] != k) {
            return 0;
        }

        //从k点向前向后遍历计数
        int count = 0;
        int cur = mid;
        while (cur < array.length && array[cur] == k) {
            count++;
            cur++;
        }
        cur = mid - 1;
        while (cur >= 0 && array[cur] == k) {
            count++;
            cur--;
        }

        return count;
    }
}