数字在排序数组中出现的次数
题目：统计一个数字在排序数组中出现的次数。例如输入排序数组{1，2，3，3，3，3，4，5}和数字3，由于3在这个数组中出现了4次，因此输出4.
找到排序数组中的第一个K：
int GetFirstK(int *data, int length, int k, int start, int end)
{
if(start > end)
return -1;
int middleIndex = start + ((end - start) >> 1);
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);
}找到排序数组中最后一个k：
int GetLastK(int *data, int length, int k, int start, int end)
{
if(start > end)
return -1;
int middleIndex = start + ((end - start) >> 1);
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);
}在分别找到第一个k和最后一个k的下标之后，就能计算出k在数组中出现的次数了。相应的代码如下：
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;
}完整代码如下：
int GetFirstK(int *data, int length, int k, int start, int end)
{
if(start > end)
return -1;
int middleIndex = start + ((end - start) >> 1);
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) >> 1);
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;
}本文参与 腾讯云自媒体分享计划，分享自作者个人站点/博客。
原始发表：2014-04-03 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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