結果

問題 No.595 登山
ユーザー qwewe
提出日時 2025-05-14 13:26:20
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
WA  
実行時間 -
コード長 2,160 bytes
コンパイル時間 646 ms
コンパイル使用メモリ 76,264 KB
実行使用メモリ 8,064 KB
最終ジャッジ日時 2025-05-14 13:27:18
合計ジャッジ時間 2,430 ms
ジャッジサーバーID
（参考情報） 		judge3 / judge4
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ファイルパターン 結果
sample AC * 4
other AC * 4 WA * 21
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ソースコード

diff # 

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

// A large enough value for infinity, considering N * max_H_diff or (N-1)*P
// Max N = 2e5, Max H_diff = 1e9 -> 2e14
// Max P = 1e9, (N-1)*P approx 2e5 * 1e9 = 2e14
const long long INF = 4e14 + 7; 

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int n;
    long long p;
    cin >> n >> p;

    vector<long long> h(n);
    for (int i = 0; i < n; ++i) {
        cin >> h[i];
    }

    // Constraints state N >= 2. If N=1 was allowed, cost is 0.
    // if (n == 1) {
    //     cout << 0 << endl;
    //     return 0;
    // }

    // pre_walk_cost[i] = min cost to walk from location 0 to location i
    vector<long long> pre_walk_cost(n);
    pre_walk_cost[0] = 0; 
    for (int i = 0; i < n - 1; ++i) {
        pre_walk_cost[i + 1] = pre_walk_cost[i] + max(0LL, h[i + 1] - h[i]);
    }

    // suf_walk_cost[i] = min cost to walk from location n-1 to location i (backwards)
    vector<long long> suf_walk_cost(n);
    suf_walk_cost[n - 1] = 0;
    for (int i = n - 2; i >= 0; --i) {
        suf_walk_cost[i] = suf_walk_cost[i + 1] + max(0LL, h[i] - h[i + 1]);
    }

    long long min_total_cost = INF;

    // Strategy 1: 0 teleports, walk 0 -> n-1
    // All locations {0, ..., n-1} are visited.
    min_total_cost = pre_walk_cost[n - 1];

    // Strategy 2: 1 teleport
    // Walk 0..k, teleport from k to n-1, then walk (n-1)..(k+1).
    // This covers locations {0, ..., k} and {k+1, ..., n-1}.
    // k is the 0-indexed end location of the first segment.
    for (int k = 0; k < n - 1; ++k) { 
        long long current_strategy_cost = pre_walk_cost[k] + p + suf_walk_cost[k + 1];
        min_total_cost = min(min_total_cost, current_strategy_cost);
    }
    
    // Strategy 3: N-1 teleports (to visit N-1 new locations after starting at loc 0)
    // Start at 0. Teleport to 1 (cost P), then from 1 to 2 (cost P), ..., then from n-2 to n-1 (cost P).
    // This requires (n-1) teleports.
    // (N-1)*P can be 0 if P=0.
    min_total_cost = min(min_total_cost, (long long)(n - 1) * p);


    cout << min_total_cost << endl;

    return 0;
}
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