Amazon Question: Run Length Encoding

Problem: Convert a string into it's Run Length Encoded String. For example run length encoded string of AABBBCCCCD is A2B3C4D1.

Solution: 

void RLE(char* str)
{
if(!str)
return;
int len = std::strlen(str);
if(len == 0 || len == 1)
return;

int count = 1;
int spaces = 0;
char currChar = str[0];
int j = 0;
for(int i = 1; i < len; ++i)
{
if(str[i] == currChar)
{
++count;
}
else
{
str[j++] = currChar;
if(count > 1)
{
char *countStr = intToStr(count);
int lenCountStr = strlen(countStr);

for(int k = 0; k < lenCountStr; ++k)
str[j++] = countStr[k];
delete [] countStr;
countStr = 0;
count = 1;
}
else
++spaces;
currChar = str[i];
}
}
str[j++] = currChar;
if(count > 1)
{
char *countStr = intToStr(count);
int lenCountStr = strlen(countStr);
for(int k = 0; k < lenCountStr; ++k)
str[j++] = countStr[k];
delete [] countStr;
countStr = 0;
}
else
++spaces;
if(j + spaces <= len)
{
str[j + spaces] = '\0';
bool getInt = false;
for(int i = j - 1, k = j + spaces - 1; i >= 0; --i)
{
if(str[i] < '0' || str[i] > '9')
{
if(!getInt)
{
str[k--] = '1';
}
str[k--] = str[i];
getInt = false;
}
else
{
str[k--] = str[i];
getInt = true;
}
}
}
else
str[j] = '\0';
}

Complexity: O(n)