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;

}