F - Distance Sums

https://atcoder.jp/contests/arc103/submissions/36976350

AtCoder/ARC103/F/F.cpp

@@ -0,0 +1,56 @@
+#include <iostream>
+#include <algorithm>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, siz[N];
+long long dis;
+std::pair<long long, int> d[N];
+std::vector<std::pair<int, int>> ans;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> d[i].first;
+
+        d[i].second = i;
+    }
+
+    std::fill(siz + 1, siz + 1 + n, 1);
+    std::sort(d + 1, d + 1 + n);
+
+    for (int i = n; i > 1; i--) {
+        long long t = d[i].first - n + (siz[i] << 1);
+        int p = std::lower_bound(d + 1, d + 1 + n, std::make_pair(t, 0)) - d;
+
+        if (d[p].first != t) {
+            cout << -1 << endl;
+
+            exit(0);
+        }
+
+        ans.emplace_back(d[i].second, d[p].second);
+        siz[p] += siz[i];
+        dis += siz[i];
+    }
+
+    if (dis != d[1].first) {
+        cout << -1 << endl;
+    } else {
+        for (auto e : ans) {
+            cout << e.first << ' ' << e.second << endl;
+        }
+    }
+
+    return 0;
+}