If i, j is not mutual, at least one of the equalities love[i]=j or love[j]=i is false. Consider the iteration where i is the smaller index of the two. If love[i] ≠ j → the algorithm’s first condition ( j = love[i] ) fails. If love[i] = j but love[j] ≠ i → the second condition fails. Thus the counter is never increased for this unordered pair. ∎ Theorem After processing a test case, mutualPairs equals the total number of mutual‑love pairs in the group.
long long ans = 0; // up to N/2 fits in int, but long long is safe for (int i = 1; i <= N; ++i) int j = love[i]; if (i < j && love[j] == i) ++ans; // count each 2‑cycle once cout << ans << '\n'; return 0; 412. Sislovesme
Multiple test cases are given. T // number of test cases (1 ≤ T ≤ 20) N // number of people (1 ≤ N ≤ 10^5) love[1] love[2] … love[N] // N integers, 1 ≤ love[i] ≤ N The sum of N over all test cases does not exceed 10^6 . Output For each test case output a single line containing the number of mutual‑love pairs. Sample Input If i, j is not mutual, at least
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