B - Shoe Shuffling

https://codeforces.com/contest/1691/submission/159005479

Codeforces/1691/B/B.cpp

@@ -0,0 +1,57 @@
+#include <iostream>
+#include <unordered_map>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int t, n, a[N];
+std::unordered_map<int, std::vector<int>> map;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> t;
+
+    while (t--) {
+        map.clear();
+
+        cin >> n;
+
+        for (int i = 1; i <= n; i++) {
+            cin >> a[i];
+
+            map[a[i]].push_back(i);
+        }
+
+        bool flag = true;
+
+        for (auto it : map) {
+            if (it.second.size() < 2) {
+                flag = false;
+                break;
+            }
+        }
+
+        if (flag) {
+            for (int i = 1; i <= n; i++) {
+                if (map[a[i]].size() > 1) {
+                    cout << map[a[i]][1] << ' ';
+                    map[a[i]].erase(map[a[i]].begin() + 1);
+                } else {
+                    cout << map[a[i]][0] << ' ';
+                    map[a[i]].clear();
+                }
+            }
+            cout << endl;
+        } else {
+            cout << -1 << endl;
+        }
+    }
+
+    return 0;
+}