学步园

#include<iostream>
#include<string.h>
using namespace std;
char * DeleteEntry(char * str)
{
     char * pstr1 = str;
     char * pstr2 = str;
     int  len = 0;
     int BeginEntryNum = 0;
     int EndEntryNum = 0;
     int BeginFlag = 0;
     while (*pstr1 != '\0')
     {
           len++;
           if(*pstr1 == ' ' && BeginFlag == 0)
                     BeginEntryNum ++;
           else
                     BeginFlag=1;
                     
           if(*pstr1 == ' ')
                    EndEntryNum++;
           else 
                    EndEntryNum = 0;
           pstr1++;
     }
     
     pstr2[len-EndEntryNum] = '\0';
     return pstr2+BeginEntryNum;
}

int main ()
{
    char str[]="  hel  lo  ";
    cout<<str<<endl;
    cout<<strlen(str)<<endl;
    char * pstr = DeleteEntry(str);
    cout<<pstr<<endl;
    cout<<strlen(pstr)<<endl;
    system("pause");
    return 0;
}

题目要求时间复杂度 最小。 功能函数不能使用系统提供的函数。