Codeforces #631 Dreamoon Likes Coloring

#include <bits/stdc++.h>
#define ll long long
using namespace std;

const int maxn = 1e5 + 5;

int t, n, m, a[maxn], b[maxn];

int main()
{
    cin >> n >> m;
    int k = n - m;
    ll sum = 0;
    for (int i = 1; i <= m; ++i) cin >> a[i], sum += a[i];
    if (sum < n) {puts("-1"); return 0;}
    b[m] = n - a[m] + 1;
    for (int i = m - 1; i; --i)
    {
        b[i] = b[i + 1] - 1;
        if (n - b[i] + 1 < a[i]) b[i] = n - a[i] + 1;
    }
    if (b[1] < 1) {puts("-1"); return 0;}
    if (b[1] != 1)
    {
        b[1] = 1;
        for (int i = 2; i <= m; ++i)
            if (b[i] - b[i - 1] > a[i - 1]) b[i] = b[i - 1] + a[i - 1];
            else break;
    }
    for (int i = 1; i <= m; ++i) cout << b[i] << ‘ ‘;
    return 0;
}