Min Flips to make alternate 0's & 1's

char flip(char ch) {
    return ( ch == '0') ? '1' : '0';
}

int minFlips(string str, char expected) {
    int count = 0;
    for (int i=0; i<str.length(); i++) {
        if (str[i] != expected) {
            count ++;
        }
        expected = flip(expected);
    }
    return count;
}

int minFlips (string S)
{
    return min(minFlips(S, '1'), minFlips(S, '0'));
}