Today I have done leetcode's March LeetCoding Challenge with cpp.

March LeetCoding Challenge 31

Description

Put Marbles in Bags

You have k bags. You are given a 0-indexed integer array weights where weights[i] is the weight of the ith marble. You are also given the integer k.

Divide the marbles into the k bags according to the following rules:

• No bag is empty.
• If the ith marble and jth marble are in a bag, then all marbles with an index between the ith and jth indices should also be in that same bag.
• If a bag consists of all the marbles with an index from i to j inclusively, then the cost of the bag is weights[i] + weights[j].

The score after distributing the marbles is the sum of the costs of all the k bags.

Return the difference between the maximum and minimum scores among marble distributions.

Example 1:

Input: weights = [1,3,5,1], k = 2
Output: 4
Explanation: 
The distribution [1],[3,5,1] results in the minimal score of (1+1) + (3+1) = 6. 
The distribution [1,3],[5,1], results in the maximal score of (1+3) + (5+1) = 10. 
Thus, we return their difference 10 - 6 = 4.

Example 2:

Input: weights = [1, 3], k = 2
Output: 0
Explanation: The only distribution possible is [1],[3]. 
Since both the maximal and minimal score are the same, we return 0.

Constraints:

• 1 <= k <= weights.length <= 105
• 1 <= weights[i] <= 109

Solution

class Solution {
public:
  long long putMarbles(vector<int>& weights, int k) {
    int len = weights.size();
    vector<int> sum(len - 1);
    sum.reserve(len - 1);
    for(int i = 1; i < len; ++i) {
      sum[i - 1] = weights[i] + weights[i - 1];
    }

    sort(sum.begin(), sum.end());
    long long answer = 0;
    auto it = sum.begin();
    auto rit = sum.rbegin();
    for(;--k; ++it, ++rit) {
      answer += *rit - *it;
    }

    return answer;
  }
};

// Accepted
// 103/103 cases passed (33 ms)
// Your runtime beats 76.79 % of cpp submissions
// Your memory usage beats 82.7 % of cpp submissions (64.3 MB)