AtCoder Beginner Contest 163

Contest link: https://atcoder.jp/contests/abc163/tasks

A - Circle Pond

#include <bits/stdc++.h>
using namespace std;
int main() {
    double r; cin >> r;
    cout << 2 * 3.14 * r;
}

B - Homework

#include <bits/stdc++.h>
using namespace std;
int main() {
    int n, m; cin >> n >> m;
    int sum = 0;
    for (int i = 0; i < m; i++) {
        int t; cin >> t;
        sum += t;
    }
    if (sum > n) cout << "-1";
    else cout<< n - sum;
}

C - management

#include <bits/stdc++.h>
using namespace std;
int main() {
    int n; cin >> n;
    int cnt[n] = {};
    for (int i = 0; i < n - 1; i++) {
        int t; cin >> t;
        ++cnt[t - 1];
    }
    for (int i : cnt) cout << i << "\n";
}

D - Sum of Large Numbers

#include <bits/stdc++.h>
#define f(n) ((n + 1LL) * (n) / 2)
using namespace std;
const int mod = 1e9 + 7;
int main() {
    int n, k; cin >> n >> k;
    long long ans = 1;
    for (int i = k; i <= n; i++) 
        ans = (ans + f(n) - f(n - i) - f(i - 1) + 1) % mod;
    cout << ans;
}