B - AND Sorting

https://codeforces.com/contest/1682/submission/158031002

Codeforces/1682/B/B.cpp

@@ -0,0 +1,30 @@
+#include <algorithm>
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+int t, n;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> t;
+
+    while (t--) {
+        cin >> n;
+
+        int ans = -1;
+
+        for (int i = 0, x; i < n; i++) {
+            cin >> x;
+
+            if (x != i) ans &= x;
+        }
+
+        cout << ans << endl;
+    }
+
+    return 0;
+}