C - The Kth Time Query

https://atcoder.jp/contests/abc235/submissions/28548889

AtCoder/ABC235/C/C.cpp

@@ -0,0 +1,28 @@
+#include <iostream>
+#include <unordered_map>
+#include <vector>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+int n, q, a, x, k;
+std::unordered_map<int, std::vector<int>> map;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin >> n >> q;
+    for (int i = 1; i <= n; i++) {
+        cin >> a;
+        map[a].push_back(i);
+    }
+    while (q--) {
+        cin >> x >> k;
+        if (!map.count(x) || map[x].size() < k) {
+            cout << -1 << endl;
+        } else {
+            cout << map[x][k - 1] << endl;
+        }
+    }
+    return 0;
+}