Problem:
Max Score: 350 Points

Problem Statement

There are N buildings along the line. The i-th building from the left is colored in color i, and its height is currently a_i meters.

Chokudai is a mayor of the city, and he loves colorful thigs. And now he wants to see at least K buildings from the left.

You can increase height of buildings, but it costs 1 yens to increase 1 meters. It means you cannot make building that height is not integer.

You cannot decrease height of buildings.

Calculate the minimum cost of satisfying Chokudai's objective.

Note: "Building i can see from the left" means there are no j exists that (height of building j) ≥ (height of building i) and j < i.

Input Format

N K
a_1 a_2 a_3 ... a_N

Output Format

Print the minimum cost in one line. In the end put a line break.

Constraints

1 ≤ K ≤ N ≤ 15

1 ≤ a_i ≤ 10^9

Scoring

Subtask 1 [120 points]

N = K

Subtask 2 [90 points]

N ≤ 5

a_i ≤ 7

Subtask 3 [140 points]

There are no additional constraints.

Sample Input 1

5 5
3949 3774 3598 3469 3424

Sample Output 1

1541

The optimal solution is (height of buildings from the left) = [3949, 3950, 3951, 3952, 3953].

Sample Input 2

5 3
7 4 2 6 4

Sample Output 2

7

The optimal solution is (height of buildings from the left) = [7, 8, 2, 9, 4].

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
    int N,K; cin >> N >> K;
    vector<ll> a(N),b(N);
    for (int i=0;i<N;i++) cin >> a[i];
    ll res = 1e11;
    for (int bit=0;bit<(1<<N);bit++){
        b = a; 
        ll s = 0;
        ll max_h = b[0];
        ll num_color = 1;
        for (int i=1;i<N;i++){
            if (!(bit & (1<<i))) continue;
            num_color++;
            if (b[i]<=max_h){
                s += max_h + 1 - b[i];
                b[i] = max_h + 1;
                max_h = b[i];
            }
        }
        if (num_color==K) res = min(res,s);
    }
    cout << res << endl;
    return 0;
}