Submission #1086938

#	Time	Username	Problem	Language	Result	Execution time	Memory
1086938		codexistent	Boxes with souvenirs (IOI15_boxes)	C++14	10 / 100	1 ms	2396 KiB

boxes

// Key to solution lies in the fact that you cannot have more than 1 full-circle trip.
// PROOF: Assume you have 2 full-circle trips. Then you travel 2L time and deliver >= 2K souvenirs.
//        But we can easily just deliver the first k souvenirs(from clockwise direction) in 2 * x time going 
//        clockwise and deliver the first k souvenirs(from counter-clockwise direction) in at most 2 * (l - x)
//        time going counter-clockwise, which is just as good if not better. □

#include "boxes.h"
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define MAXN 10000005
#define FOR(i, a, b) for(ll i = a; i <= b; i++)
#define RFOR(i, a, b) for(ll i = a; i >= b; i--)

ll dp_cw[MAXN], dp_ccw[MAXN], r = __LONG_LONG_MAX__;

long long delivery(int N, int K, int L, int p[]) {
    dp_cw[0] = dp_ccw[N + 1] = 0;
    FOR(i, 1, N) dp_cw[i] = dp_cw[max(0ll, i - K)] + 2 * p[i - 1];
    RFOR(i, N, 1) dp_ccw[i] = dp_ccw[min((ll)N + 1, i + K)] + 2 * (L - p[i - 1]);

    FOR(i, 0, N) r = min(r, dp_cw[i] + dp_ccw[i + 1]);
    if(N >= K) FOR(i, 0, N) r = min(r, dp_cw[i] + dp_ccw[i + K + 1] + 2 * L);

    return r;
}

• Subtask 1: 10 / 10
• Subtask 2: 0 / 10
• Subtask 3: 0 / 15
• Subtask 4: 0 / 15
• Subtask 5: 0 / 20
• Subtask 6: 0 / 30