Codeforces 420D. Cup Trick

#include <cstdio>
#include <ext/pb_ds/assoc_container.hpp>
#include <algorithm>
const int N = 2e6 + 100;
int n, m;
__gnu_pbds::tree<int,
__gnu_pbds::null_type,
       std::less<int>,
__gnu_pbds::rb_tree_tag,
__gnu_pbds::tree_order_statistics_node_update> pos;
int val[N], used[N], ans[N];

int main() {
    scanf("%d%d", &n, &m);
    for (int i = m + 1; i <= n + m; ++i)
        pos.insert(i);
    for (int i = 1; i <= m; ++i) {
        int x, y;
        scanf("%d%d", &x, &y);
        auto p = pos.find_by_order(y - 1);
        pos.erase(p);
        int t = *p;
        if (!val[t]) {
            ans[t - m] = x;
            if (used[x]) return puts("-1"), 0;
            used[x] = true;
            val[m - i] = x;
            t = m - i;
        } else {
            if (val[t] != x) return puts("-1"), 0;
            val[m - i] = val[t];
            t = m - i;
        }
        pos.insert(t);
    }
    int t = 1;
    for (int i = 1; i <= n; ++i)
        if (!ans[i]) {
            while (used[t]) ++t;
            ans[i] = t++;
        }
    for (int i = 1; i <= n; ++i)
        printf("%d ", ans[i]);
    puts("");

    return 0;
}