Find longest run of a letter in a string

Write a function that returns the longest run of a letter in a string. e.g. cccc in the string abccccdef.

Answer:
O(n) solution which sweeps thru the array..

cur next
 |  |
accccefgggggg

GetRepSeq(const char* str, char **start, size_t *len)
{
    const char* next = str + 1;
    const char* cur = str;
    size_t cur_len = 1;
    *start = 0;
    *len = 1;
    while (*next)
    {
        if ( *next == *cur )
        {
            ++next;
            ++cur_len;
        }
        else
        {
            /* we just encountered a non equal char */
            if ( cur_len >= *len )
            {
                *len = cur_len;
                *start = cur;
            }
            cur = next;
            ++next;
        }
    }
}

Alternative Answer : Sufix trees