AtCoder Beginner Contest 206（Sponsored by Panasonic）

AtCoder Beginner Contest 206（Sponsored by Panasonic）

A - Maxi-Buying

int main() {
    IOS; int x; cin >> x; x = floor(x * 1.08);
    if (x < 206) cout << "Yay!";
    else if (x == 206) cout << "so-so";
    else cout << ":(";
    return 0;
}

B - Savings

int main() {
    IOS; ll x; cin >> x;
    ll s = floor(sqrt(x <<= 1));
    cout << (s * (s + 1) >= x ? s : s + 1);
    return 0;
}

C - Swappable

int main() {
    IOS; map<int, int> st; cin >> n;
    rep (i, 1, n) {
        cin >> m; ++st[m];
        ans += i - st[m];
    }
    cout << ans;
    return 0;
}

D - KAIBUNsyo

int f[N], a[N];

int ff(int x) { return f[x] == x ? x : f[x] = ff(f[x]); }

void unit(int x, int y) { if ((x = ff(x)) ^ (y = ff(y))) f[y] = x; }

int main() {
    IOS; cin >> n;
    rep (i, 1, n) cin >> a[i], f[a[i]] = a[i];
    rep (i, 1, n >> 1) {
        a[i] = ff(a[i]), a[n + 1 - i] = ff(a[n + 1- i]);
        if (a[i] ^ a[n + 1 - i]) unit(a[i], a[n + 1 - i]), ++m;
    }
    cout << m;
    return 0;
}

E - Divide Both

容斥

ll c[N], a[N], ans;

int main() {
    IOS; cin >> n >> m;
    rep (i, 2, m >> 1)
        for (int j = (n - 1) / i * i + i; j <= m; j += i) ++c[i];
    per (i, m >> 1, 2) {
        a[i] = c[i] * (c[i] - 1);
        for (int j = i * 2; j <= m; j += i) a[i] -= a[j];
        ans += a[i];
        if (i >= n) ans -= c[i] - 1 << 1;
    }
    cout << ans;
    return 0;
}