统计一个数字在排序数组中出现的次数。

剑指offer：统计一个数字在排序数组中出现的次数。

思路：改进二分查找算法，找到第一个K出现的索引，和第最后一个k的索引。

class Solution {public:    int GetNumberOfK(vector<int> data ,int k) {        //必须先考虑边境条件        int vecLen = data.size();        if(vecLen == 0)            return 0;        //GetFirstKIndex,改良二分查找法，找到最左边K的索引int leftIndexOfK = GetFirstKIndex(data,k,vecLen);        if(leftIndexOfK == -1)//如果不存在k,返回零。            return 0;int RightIndexOfK = GetLastKIndex(data,k,vecLen);return RightIndexOfK - leftIndexOfK + 1;    } int GetFirstKIndex(vector<int> &data, int k, int length ){    int low,high,mid;low = 0;high = length - 1;while(low <= high){mid = (low + high) / 2;if(data[mid] > k)high = mid -1;else if(data[mid] < k)low = mid + 1;else if(data[mid] == k){    if(mid > 0 && data[mid - 1] != k)return mid;else if(mid == 0)return mid;else high = mid -1;}}return -1;} int GetLastKIndex(vector<int> &data, int k, int length ){    int low,high,mid;low = 0;high = length - 1;while(low <= high){mid = (low + high) / 2;if(data[mid] > k)high = mid -1;else if(data[mid] < k)low = mid + 1;else if(data[mid] == k){    if(mid < length && data[mid + 1] != k)return mid;else if(mid == length)return mid;else low = mid +1;}}return -1;}};