Special palindromic substrings

substrCount.cpp

// problem : https://www.hackerrank.com/challenges/special-palindrome-again/problem

long substrCount(int n, string s) {
    long count = 0;

    // 1st pass
    vector<pair<char, int>> v;
    char cur = 0;
    for( auto ch : s )
    {
        if( cur == ch )
        {
            ++( v.back().second );
        }
        else
        {
            cur = ch;
            v.push_back( { ch, 1 } );
        }
    }

    // 2nd pass
    for( auto& p : v )
    {
        count += ( p.second + 1 ) * p.second / 2;
    }

    // 3rd pass
    for( int i = 1; i < v.size( ) - 1; ++ i )
    {
        if( v[ i ].second == 1
            && v[ i - 1 ].first == v[ i + 1 ].first )
        {
            count += min( v[ i - 1 ].second, v[ i + 1 ].second );
        }
    }

    return count;
}