题目描述：
统计一个数字在排序数组中出现的次数。

思路：

利用二分法寻找左右端点。

代码：

代码

# -*- coding:utf-8 -*-
class Solution:
    def GetNumberOfK(self, data, k):
        # write code here
        if not data:
            return 0
        low = 0
        high = len(data) - 1
        cnt = 0
        end = len(data) - 1
        while low <= high:
            medium = (low + high) / 2
            if data[medium] == k:
                # print "medium: ", medium
                # 这个数字前面后面都可能存在我们要找的数
                while medium >= 0 and data[medium] == k:
                    medium -= 1
                medium += 1
                # print "left: ", medium
                while medium <= end and data[medium] == k:
                    medium += 1
                    cnt += 1
                return cnt
            elif data[medium] < k:
                low = medium + 1
            else:
                high = medium - 1
        return cnt