我对一个文件进行了二分搜索。该文件充满了日志消息,其中每行都以日期开头(日期或根据发生的事件排序)
示例:
- 2011-09-18 09.38.20.123
- 2011-09-18 09.38.20.245
- 2011-09-18 09.38.20.393
- 2011-09-18 09.38.20.400
- 2011-09-18 09.38.20.785
如果我需要找到这个日期,例如:2011-09-18 09.38.20.390,我的二分搜索将找不到完全匹配 - 但我不需要完全匹配,我需要找到最接近的日期(这就是我的立场)。
当前代码将在 2011-09-18 09.38.20.245 和 2011-09-18 09.38.20.393 之间跳转。
我需要一些帮助来修改以下代码,以便获得最接近的数字。在上述情况下,我希望:2011-09-18 09.38.20.245(多总比少好)
BinarySearch::BinarySearch(QString strFileName,QDateTime dtFrom_target,QDateTime dtTo_target)
{
QFile file(strFileName);
qint64 nFileSize = file.size();
int nNewFromPos;
int nNewToPos;
nNewFromPos = Search(file, dtFrom_target, nFileSize);
nNewToPos = Search(file, dtFrom_target, nFileSize);
if(nNewFromPos!=-1 && nNewToPos!=-1){
// now parse the new range
}
else{
// dates out of bound
}
}
int BinarySearch::Search(QFile &file, QDateTime dtKey, int nMax)
{
file.open(QIODevice::ReadOnly);
char lineBuffer[1024];
qint64 lineLength;
QDateTime dtMid;
int mid;
int min;
if(!min) min = 0;
while (min <= nMax)
{
mid=(min+nMax)/2; // compute mid point.
file.seek(mid); // seek to middle of file (position based on bytes)
qint64 lineLength=file.readLine(lineBuffer,sizeof(lineBuffer)); // read until \n or error
if (lineLength != -1) //something is read
{
// validate string begin (pos = 0) starts with date
lineLength = file.readLine(lineBuffer, 24); //read exactly enough chars for the date from the beginning of the log file
if(lineLength == 23)
{
dtMid = QDateTime::fromString(QString(lineBuffer),"yyyy-MM-dd HH.mm.ss.zzz"); //2011-09-15 09.38.20.192
if(dtMid.isValid())
{
if(dtKey > dtMid){
min = mid + 1;
}
else if(dtKey < dtMid){
max = mid - 1; // repeat search in bottom half.
}
else{
return mid; // found it. return position
}
}
}
}
}
return -1; // failed to find key
}
最佳答案
尝试实现相当于 std::equal_range
的算法它返回一对结果 std::lower_bound
和 std::upper_bound
- 查找排序范围内第一个不小于该值(下限)的元素的位置
- 查找排序范围中第一个大于该值(上限)的元素的位置
--
template<typename OutIter>
void ReadLogsInRange(
std::istream& logStream, Log::Date from, Log::Date to, OutIter out)
{
Log l = LowerBound(logStream, from);
*out++ = l;
while(logStream >> l && l.date < to)
*out++ = l;
}
关于c++ 对日期进行二分搜索排序 -> 我需要一个范围(cca),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/7554427/