有序数组中数字出现次数

题目：统计有序数组中排序某一个数出现的次数
比如:{1, 2,2,2,3 ,4 , 5}中，2出现了3次，3出现了0次


思路：
利用二分查找，找到某一个数在数组中出现的第一个下标firstIndex和最后一个下标lastIndex
出现次数就是：lastIndex - firstIndex + 1

#include <iostream>
using namespace std;

#define NSIZ 100


int GetFirsIndex(int data[], int n, int key)
{
	int left = 0;
	int right = n - 1;
	int mid = 0;

	while(left <= right)
	{
		mid = left + (right - left) /2 ;

		if (data[mid] == key)
		{
			if (mid > 0 && data[mid - 1] != key || mid == 0)
			{
				return mid;
			}
			else
			{
				right = mid - 1;
			}
		}
		else if (data[mid] < key)
		{
			left = mid + 1;
		}
		else
		{
			right = mid - 1;
		}

	}

	return -1;
}

int GetLastIndex(int data[], int n, int key)
{
	int left = 0;
	int right = n - 1;
	int mid = 0;

	while(left <= right)
	{
		mid = left + (right - left) /2 ;

		if (data[mid] == key)
		{
			if (mid < n-1 && data[mid + 1] != key || mid == (n-1))
			{
				return mid;
			}
			else
			{
				left = mid  + 1;
			}
		}
		else if (data[mid] < key)
		{
			left = mid + 1;
		}
		else
		{
			right = mid - 1;
		}

	}

	return -1;
}

int getNum(int data[], int n, int key)
{
	int first = GetFirsIndex(data, n, key);
	int last = GetLastIndex(data, n, key);

	if (first != -1 && last != -1)
	{
		return last - first + 1;
	}

	return 0;
}

int main()
{
	int data[] = {1, 2,2,2,3 ,4 , 5};
	int n = sizeof(data)/sizeof(data[0]);
	int key = 2;

	printf("Key:%d 个数：%d\n",key, getNum(data, n, key));
	return 0;
}