38.数字在排序数组中出现的次数

半段查找。

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