Codeforces Round #230 (Div. 2): solved A, B and D during the contest and C afterwards (http://codeforces.com/contest/393).

A.cpp

// Problem A - Nineteen
// http://codeforces.com/contest/393/problem/A

#include <string>
#include <cstdlib>
#include <iostream>
#include <algorithm>

int cnt[256];

using namespace std;

int main()
{
    string word;

    cin >> word;

    for (int i = 0; i < word.size(); ++i)
        ++cnt[word[i]];

    int ans = cnt['i'];

    ans = min(ans, cnt['t']);
    ans = min(ans, (cnt['n'] - 1) / 2);
    ans = min(ans, cnt['e'] / 3);

    cout << ans << endl;

    return EXIT_SUCCESS;
}

B.cpp

// Problem B - Three matrices
// http://codeforces.com/contest/393/problem/B

#include <cmath>
#include <cstdlib>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 222;

int n;
double mat[N][N];

int main()
{
    cin >> n;

    for (int i = 0; i < n; ++i)
        for (int j = 0; j < n; ++j)
            cin >> mat[i][j];

    // Print matrix A
    for (int i = 0; i < n; ++i)
    {
        for (int j = 0; j < n; ++j)
        {
            if (i == j)
                cout << mat[i][j];
            else
                cout << (mat[i][j] + mat[j][i]) / 2.0;

            if (j < n - 1)
                cout << ' ';
            else
                cout << endl;
        }
    }

    // Print matrix B
    for (int i = 0; i < n; ++i)
    {
        for (int j = 0; j < n; ++j)
        {
            if (i == j)
                cout << '0';
            else
                cout << (mat[i][j] - mat[j][i]) / 2.0;

            if (j < n - 1)
                cout << ' ';
            else
                cout << endl;
        }
    }

    return EXIT_SUCCESS;
}

C.cpp

// Problem C - Blocked Points
// http://codeforces.com/contest/393/problem/C

#include <cmath>
#include <cstdlib>
#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
    long long n, n2, ix, iy, t, d, ans = 0;

    cin >> n;

    if (n >= 1)
    {
        n2 = n * n;

        iy = n;

        for (long long i = 0; i <= n; ++i)
        {
            t = n2 - i * i;

            for (ix = iy; ix >= 0; --ix)
                if (ix * ix <= t)
                    break;

            // clog << i << ':' << ix << endl;

            d = iy - ix;

            if (d <= 1)
                ans += 1;
            else
                ans += d;

            iy = ix;
        }

        ans -= 1;
        ans *= 4;

        cout << ans << endl;
    }
    else
    {
        cout << 1 << endl;
    }

    return EXIT_SUCCESS;
}

D.cpp

// Problem D - Tower of Hanoi
// http://codeforces.com/contest/393/problem/D

#include <cmath>
#include <cstdlib>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 44;

int mat[3][3];
long long dp[N][3][3];

inline void relax(int k)
{
    for (int b = 0; b < 3; ++b)
    {
        for (int a = 0; a < 3; ++a)
        {
            if (a == b)
                continue;

            for (int c = 0; c < 3; ++c)
            {
                if (a == c || b == c)
                    continue;

                dp[k][a][c] = min(dp[k][a][c], dp[k][a][b] + dp[k][b][c]);
            }
        }
    }
}

long long calc(int n)
{
    if (n == 0)
        return 0;

    // This statement was not deleted during the contest so it got WA.
    // But after removing this, the solution got passed.
    // if (n == 1)
    //     return mat[0][2];

    for (int i = 0; i < 3; ++i)
        for (int j = 0; j < 3; ++j)
            dp[1][i][j] = mat[i][j];

    relax(1);

    for (int k = 2; k <= n; ++k)
    {
        for (int i = 0; i < 3; ++i)
        {
            for (int j = 0; j < 3; ++j)
            {
                if (i == j)
                    continue;

                // From a through b to c
                int a = i, c = j, b = 3 - i - j;

                long long ans1 = dp[k-1][a][b] + mat[a][c] + dp[k-1][b][c];
                long long ans2 = dp[k-1][a][c] + mat[a][b]
                               + dp[k-1][c][a] + mat[b][c] + dp[k-1][a][c];

                dp[k][a][c] = min(ans1, ans2);
            }
        }

        relax(k);
    }

    // for (int k = 0; k <= n; ++k)
    // {
    //     for (int i = 0; i < 3; ++i)
    //         for (int j = 0; j < 3; ++j)
    //             clog << dp[k][i][j] << ' ';
    //     clog << endl;
    // }

    return dp[n][0][2];
}

int main()
{
    int n;

    for (int i = 0; i < 3; ++i)
        for (int j = 0; j < 3; ++j)
            cin >> mat[i][j];
    cin >> n;

    cout << calc(n) << endl;

    return EXIT_SUCCESS;
}