Submission #656395

#	Time	Username	Problem	Language	Result	Execution time	Memory
656395		buidangnguyen05	Discharging (NOI20_discharging)	C++17	100 / 100	119 ms	37300 KiB

Discharging

#include<bits/stdc++.h>
using namespace std;

typedef long long ll;

const int N = 1e6 + 10;
int a[N]; ll f[N];

struct Line {
	ll A, B;
	Line() : A(0), B(0) {}
	Line (ll _a, ll _b) {
		A = _a, B = _b;
	}
};

struct ConvexHullTrick {
	Line st[N]; int sz, it = 1;

	long double G (Line x, Line y) {
		return 1.0 * (x.B - y.B) / (y.A - x.A);
	}

	ll calc(Line x, ll v) {
		return x.A * v + x.B;
	}

	void add(ll x, ll y) {
		Line cur = Line(x, y);
		if (sz && st[sz].A == x && st[sz].B <= y) return;
		while (sz > 1 && G(cur, st[sz]) <= G(st[sz], st[sz - 1])) --sz;
		st[++sz] = cur;
	}

	ll get(ll x) {
		if (it > sz) it = sz;
		while (it < sz && calc(st[it + 1], x) <= calc(st[it], x)) ++it;
		return calc(st[it], x);
	}
} cht;

signed main() {
	cin.tie(0)->sync_with_stdio(0);
	if (fopen("discharging.inp", "r")) {
		freopen("discharging.inp", "r", stdin);
		freopen("discharging.out", "w", stdout);
	}

	#ifdef LOCAL_MACHINE
		if (fopen("task.inp", "r")) {
			freopen("task.inp", "r", stdin);
			freopen("task.out", "w", stdout);
		}
	#endif

	int n; cin >> n;
	for (int i = 1; i <= n; ++i) cin >> a[i];

    cht.add(n, 0);
    int mx = 0;
    for (int i = 1; i <= n; ++i) {
        mx = max(mx, a[i]);
        f[i] = cht.get(mx);
        cht.add(n - i, f[i]);
    }
    cout << f[n] << "\n";
}

Compilation message (stderr)

Discharging.cpp: In function 'int main()':
Discharging.cpp:45:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   45 |   freopen("discharging.inp", "r", stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Discharging.cpp:46:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   46 |   freopen("discharging.out", "w", stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 9 / 9
• Subtask 2: 13 / 13
• Subtask 3: 25 / 25
• Subtask 4: 11 / 11
• Subtask 5: 14 / 14
• Subtask 6: 28 / 28