[OJ] Careercup Top 150(1.1): Implement an algorithm to determine if a string has all unique characters. What if you can not use additional data structures? Solution: use a character code hash table.

char_unique.cpp

static int count[256];

bool unique(const std::string& s)
{
    memset(count, 0, sizeof(count));
    const int size = s.size();
    for (int i = 0; i < size; ++i)
    {
        if (count[s[i]] > 0)
        {
            return false;
        }
        else
        {
            ++count[s[i]];
        }
    }
    return true;
}

char_unique.py

def unique(s):
    char_table = [False for _ in xrange(256)]
    
    for c in s:
        i = ord(c)
        if char_table[i]:
            return False
        else:
            char_table[i] = True
    
    return True