Submission #287966

#	Time	Username	Problem	Language	Result	Execution time	Memory
287966		PeppaPig	Discharging (NOI20_discharging)	C++14	100 / 100	181 ms	13276 KiB

Discharging

#include <bits/stdc++.h>

#define long long long

using namespace std;

const int N = 1e6 + 5;

struct CHT {
    struct line {
        long m, c;
        line(long m, long c) : m(m), c(c) {}
        long f(long x) { return m * x + c; }
    };
    vector<line> vec;

    bool bad(line a, line b, line c) {
        return 1.0 * (c.c - a.c) / (a.m - c.m) <= 1.0 * (b.c - a.c) /  (a.m - b.m);
    }

    void add(long m, long c) {
        line l(m, c);
        while(vec.size() > 1 && bad(vec[(int)vec.size() - 2], vec.back(), l))
            vec.pop_back();
        vec.emplace_back(l);
    }

    long get_ans(long x) {
        if(vec.empty()) return 1e18;
        int l = 0, r = (int)vec.size() - 1;
        while(l < r) {
            int mid = (l + r) >> 1;
            if(vec[mid].f(x) >= vec[mid + 1].f(x))
                l = mid + 1;
            else r = mid;
        }
        return vec[r].f(x);
    }
} hull;

int n, A[N];
long dp[N];
vector<int> stk;

int main() {
    scanf("%d", &n);
    for(int i = n; i; i--) scanf("%d", A + i);

    for(int i = 1; i <= n; i++) {
        while(!stk.empty() && A[stk.back()] <= A[i])
            stk.pop_back();
        stk.emplace_back(i);
    }
    for(int i = 0; i < (int)stk.size(); i++) {
        hull.add(A[stk[i]], dp[i - 1]);
        dp[i] = hull.get_ans(stk[i]);
    }

    printf("%lld\n", dp[(int)stk.size() - 1]);

    return 0;
}

Compilation message (stderr)

Discharging.cpp: In function 'int main()':
Discharging.cpp:46:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   46 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
Discharging.cpp:47:33: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   47 |     for(int i = n; i; i--) scanf("%d", A + i);
      |                            ~~~~~^~~~~~~~~~~~~

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