劍指offer——數字在排序數組中出現的次數

經過二分查找，找到k在數組中第一次出現的位置和最後一次出現的位置。

#include <iostream>
using namespace std;

int GetFirstK(int *data,int length,int k,int start,int end)
{
	if (start>end)
	{
		return -1;
	}
	int middleIndex=start+(end-start)/2;
	int middleData=data[middleIndex];
	if (middleData==k)
	{
		if (middleIndex>0&&data[middleIndex-1]!=k||middleIndex==0)
		{
			return middleIndex;
		}
		else
		{
			end=middleIndex-1;
		}
	}
	else if(middleData>k)
	{
		end=middleIndex-1;
	}
	else
	{
		start=middleIndex+1;
	}
	return GetFirstK(data,length,k,start,end);
}

int GetLastK(int *data,int length,int k,int start,int end)
{
	if (start>end)
	{
		return -1;
	}
	int middleIndex=start+(end-start)/2;
	int middleData=data[middleIndex];
	if (middleData==k)
	{
		if (middleIndex<length-1&&data[middleIndex+1]!=k||middleIndex==0)
		{
			return middleIndex;
		}
		else
		{
			start=middleIndex+1;
		}
	}
	else if(middleData>k)
	{
		end=middleIndex-1;
	}
	else
	{
		start=middleIndex+1;
	}
	return GetLastK(data,length,k,start,end);
}

int GetNumberOfK(int* data,int length,int k)
{
	int number=0;
	if (data!=NULL&&length>0)
	{
		int first=GetFirstK(data,length,k,0,length-1);
		int last=GetLastK(data,length,k,0,length-1);
		if (first>-1&&last>-1)
		{
			number=last-first+1;
		}	
	}
	return number;
}

int main()
{
	int a[]={1,2,2,2,3,3,3,3,3,3,4,4,5,6};
	cout<<GetNumberOfK(a,14,3)<<endl;
	return 0;
}