面试题32：数字在排序数组中出现的次数

#include "stdafx.h"
#include <iostream>
#include <assert.h>
using namespace std;

//找到数组中第一次出现key的元素的下标
int BinarySearchFirstKey(int nArr[], int nLength, int key)
{
assert(nArr != NULL && nLength > 0);
int nLow = 0;
int nHigh = nLength - 1;
int nMid = 0;

while (nLow <= nHigh)
{
nMid = nLow + ((nHigh - nLow) >> 1);
if (nArr[nMid] >= key)
{
nHigh = nMid - 1;
}
else
{
nLow = nMid + 1;
}
}

if (nLow >= 0 && nLow < nLength && nArr[nLow] == key)
{
return nLow;
}
else
{
return -1;
}
}

//找到数组中最后一次出现key的元素的下标
int BinarySearchLastKey(int nArr[], int nLength, int key)
{
assert(nArr != NULL && nLength > 0);
int nLow = 0;
int nHigh = nLength - 1;
int nMid = 0;

while (nLow <= nHigh)
{
nMid = nLow + ((nHigh - nLow) >> 1);
if (nArr[nMid] > key)
{
nHigh = nMid - 1;
}
else
{
nLow = nMid + 1;
}
}

if (nHigh >= 0 && nHigh < nLength && nArr[nHigh] == key)
{
return nHigh;
}
else
{
return -1;
}
}

int GetNumberOfKey(int nArr[], int nLength, int key)
{
assert(nArr != NULL && nLength > 0);
if (BinarySearchFirstKey(nArr, nLength, key) != -1)
{
return BinarySearchLastKey(nArr, nLength, key) - BinarySearchFirstKey(nArr, nLength, key) + 1;
}
else
{
return -1;
}
}

int _tmain(int argc, _TCHAR* argv[])
{
int nArr[8] = {1,2,3,3,3,3,4,5};
int key = 0;
cin >> key;
cout << GetNumberOfKey(nArr, 8, key) << endl;
system("pause");
return 0;
}