Submission #708195

#	Time	Username	Problem	Language	Result	Execution time	Memory
708195		Cyanmond	Ancient Books (IOI17_books)	C++17	50 / 100	129 ms	30516 KiB

books

#include "books.h"
#include <bits/stdc++.h>

using i64 = long long;
constexpr i64 inf = 1ll << 50;

void chmax(i64 &a, i64 b) {
    if (a < b) a = b;
}

long long minimum_walk(std::vector<int> p, int s) {
    const int n = (int)p.size();
    std::vector<i64> imos(n), imos2(n);
    for (int i = 0; i < n; ++i) {
        int a = i, b = p[i];
        if (a > b) std::swap(a, b);
        ++imos[a];
        --imos[b];
        if (a != b) {
            ++imos2[a + 1];
            --imos2[b];
        }
    }
    for (int i = 0; i < n - 1; ++i) {
        imos[i + 1] += imos[i];
        imos2[i + 1] += imos2[i];
    }
    i64 baseCost = std::accumulate(imos.begin(), imos.end(), 0ll);

    auto solve = [&](const int f) {
        i64 x = 0, c = 0;
        for (int i = f; i < n; ++i) {
            if (imos[i] == 0) {
                ++c;
            }
            if (imos[i] != 0) {
                x += c;
                c = 0;
            }
        }
        c = 0;
        for (int i = f - 1; i >= 0; --i) {
            if (imos[i] == 0) {
                ++c;
            }
            if (imos[i] != 0) {
                x += c;
                c = 0;
            }
        }
        return x;
    };
    i64 answer = inf;
    for (int i = s; i < n; ++i) {
        if (imos2[i] == 0) {
            answer = std::min(answer, baseCost + 2 * solve(i));
            break;
        }
    }
    for (int i = s; i >= 0; --i) {
        if (imos2[i] == 0) {
            answer = std::min(answer, baseCost + 2 * solve(i));
            break;
        }
    }
    return answer;
}

• Subtask 1: 12 / 12
• Subtask 2: 10 / 10
• Subtask 3: 28 / 28
• Subtask 4: 0 / 20
• Subtask 5: 0 / 30