AtCoder Beginner Contest 371 E(思维 + 计数)

题意

题解

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#include <bits/stdc++.h>using i64 = long long;int main() {std::ios::sync_with_stdio(false);std::cin.tie(nullptr);int N;std::cin >> N;i64 ans = 0;std::vector<int> A(N + 1), lst(N + 1);for (int i = 1; i <= N; i++) {std::cin >> A[i];ans += i64(i - lst[A[i]]) * (N - i + 1);lst[A[i]] = i;}std::cout << ans << "\n";return 0;
}