124 lines
2.5 KiB
C++
124 lines
2.5 KiB
C++
/* Problem URL: https://codeforces.com/contest/976/problem/D */
|
|
|
|
#include <bits/stdc++.h>
|
|
#include <ext/pb_ds/assoc_container.hpp>
|
|
#include <ext/pb_ds/tree_policy.hpp>
|
|
|
|
using namespace std;
|
|
using namespace __gnu_pbds;
|
|
|
|
template <class T, class comp = less<>>
|
|
using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
|
|
|
|
#define V vector
|
|
|
|
#define rmin(a, b) a = min(a, b)
|
|
#define rmax(a, b) a = max(a, b)
|
|
|
|
#define rep(i, lim) for (int i = 0; i < (lim); i++)
|
|
#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
|
|
|
|
#define repv(i, v) for (auto &i : (v))
|
|
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
|
|
#define sortv(v) sort(v.begin(), v.end())
|
|
#define all(v) (v).begin(), (v).end()
|
|
|
|
using vi = vector<int>;
|
|
using vvi = vector<vi>;
|
|
using vvvi = vector<vvi>;
|
|
using vvvvi = vector<vvvi>;
|
|
|
|
using ll = long long;
|
|
|
|
using vl = vector<ll>;
|
|
using vvl = vector<vl>;
|
|
using vvvl = vector<vvl>;
|
|
using vvvvl = vector<vvvl>;
|
|
|
|
template<class v>
|
|
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
|
|
os << vec[0];
|
|
for (size_t i = 1; i < vec.size(); i++) {
|
|
os << ' ' << vec[i];
|
|
}
|
|
os << '\n';
|
|
return os;
|
|
}
|
|
|
|
template<class v>
|
|
auto operator>>(istream &is, vector<v> &vec)->istream& {
|
|
for (auto &i : vec) {
|
|
is >> i;
|
|
}
|
|
return is;
|
|
}
|
|
|
|
template<class v>
|
|
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
|
|
for (auto &i : vec) {
|
|
os << i[0];
|
|
for (size_t j = 1; j < i.size(); j++) {
|
|
os << ' ' << i[j];
|
|
}
|
|
os << '\n';
|
|
}
|
|
return os;
|
|
}
|
|
|
|
template<class v>
|
|
auto operator>>(istream &is, vector<vector<v>> &vec)->istream& {
|
|
for (auto &i : vec) {
|
|
for (auto &j : i) {
|
|
is >> j;
|
|
}
|
|
}
|
|
return is;
|
|
}
|
|
|
|
int main()
|
|
{
|
|
ios::sync_with_stdio(false);
|
|
cin.tie(nullptr);
|
|
|
|
int size;
|
|
cin >> size;
|
|
|
|
vi fds(size);
|
|
cin >> fds;
|
|
|
|
int n = fds.back() + 1;
|
|
|
|
vi ans(n, fds.back());
|
|
rep(i, fds.size()) {
|
|
ans[i] = fds[fds.size() - i - 1];
|
|
}
|
|
nrep(i, fds.size(), n) {
|
|
ans[i] = fds[0];
|
|
}
|
|
|
|
V<pair<int, int>> edges;
|
|
int valid = n - 1;
|
|
|
|
rep(i, n) {
|
|
if (ans[i] == 0) {
|
|
break;
|
|
}
|
|
|
|
int now = valid;
|
|
while (ans[i] != 0) {
|
|
ans[i]--;
|
|
ans[now]--;
|
|
edges.emplace_back(i + 1, now + 1);
|
|
if (ans[now] == 0) {
|
|
valid = now - 1;
|
|
}
|
|
now--;
|
|
}
|
|
}
|
|
|
|
cout << edges.size() << '\n';
|
|
repv(i, edges) {
|
|
cout << i.first << ' ' << i.second << '\n';
|
|
}
|
|
}
|