1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
#include <iostream>
using namespace std;
int const maxN = 50003;
int level[maxN];
long long sand_used = 0;

void change_level(int pos, int target) {
    sand_used += target - level[pos];
    level[pos] = target;
}

int main()
{
    int n, k;
    cin >> n >> k;
    for (int i = 0; i < n; i++) {
        cin >> level[i];
        level[i] += i * k;
    }

    for (int i = 1; i < n; i++) {
        if (level[i] < level[i - 1]) {
            change_level(i, level[i - 1]);
            continue;
        }
        if (level[i] > level[i - 1] + 2 * k) {
            int target = level[i] - 2 * k;
            for (int j = i - 1; j >= 0; j--) {
                if (level[j] < target) {
                    change_level(j, target);
                }
                else {
                    break;
                }
                target -= 2*k;
            }
        }
    }
    cout << sand_used;
}