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Luogu/P1121/P1121.cpp
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80
Luogu/P1121/P1121.cpp
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#include <iostream>
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#include <algorithm>
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#include <limits>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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const int N = 2e5 + 5;
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int n, a[N];
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bool flag = true;
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long long sum, s_max[N], s_min[N], f_max[N], f_min[N], g_max[N], g_min[N], ans;
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> n;
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for (int i = 1; i <= n; i++) {
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cin >> a[i];
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sum += a[i];
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flag &= a[i] < 0;
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}
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if (flag) {
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std::sort(a + 1, a + 1 + n);
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cout << a[n] + a[n - 1] << endl;
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exit(0);
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}
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ans = std::numeric_limits<int>::min();
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std::fill_n(s_max, N, std::numeric_limits<int>::min());
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std::fill_n(s_min, N, std::numeric_limits<int>::max());
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std::fill_n(f_max, N, std::numeric_limits<int>::min());
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std::fill_n(f_min, N, std::numeric_limits<int>::max());
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std::fill_n(g_max, N, std::numeric_limits<int>::min());
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std::fill_n(g_min, N, std::numeric_limits<int>::max());
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for (int i = 1; i <= n; i++) {
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s_max[i] = std::max(s_max[i - 1] + a[i], static_cast<long long>(a[i]));
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s_min[i] = std::min(s_min[i - 1] + a[i], static_cast<long long>(a[i]));
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f_max[i] = std::max(f_max[i - 1], s_max[i]);
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f_min[i] = std::min(f_min[i - 1], s_min[i]);
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}
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std::fill_n(s_max, N, std::numeric_limits<int>::min());
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std::fill_n(s_min, N, std::numeric_limits<int>::max());
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for (int i = n; i; i--) {
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s_max[i] = std::max(s_max[i + 1] + a[i], static_cast<long long>(a[i]));
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s_min[i] = std::min(s_min[i + 1] + a[i], static_cast<long long>(a[i]));
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g_max[i] = std::max(g_max[i + 1], s_min[i]);
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g_min[i] = std::min(g_min[i + 1], s_min[i]);
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}
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std::cerr << ans << endl;
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// 不跨环
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for (int i = 1; i < n; i++) {
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ans = std::max(ans, f_max[i] + g_max[i + 1]);
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}
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std::cerr << ans << endl;
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// 跨环
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for (int i = 1; i < n; i++) {
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ans = std::max(ans, sum - (f_min[i] + g_min[i + 1]));
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}
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cout << ans << endl;
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return 0;
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}
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Luogu/P1121/data/P1121_2.in
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Luogu/P1121/data/P1121_2.out
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Luogu/P1121/data/P1121_2.out
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