LeetCode #798: Smallest Rotation with Highest Score (C/C++).

hard

source: https://leetcode.com/problems/smallest-rotation-with-highest-score/
C/C++ Solution to LeetCode problem 798. Smallest Rotation with Highest Score.

Problem

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You are given an array nums. You can rotate it by a non-negative integer k so that the array becomes [nums[k], nums[k + 1], ... nums[nums.length - 1], nums[0], nums[1], ..., nums[k-1]]. Afterward, any entries that are less than or equal to their index are worth one point.

• For example, if we have nums = [2,4,1,3,0], and we rotate by k = 2, it becomes [1,3,0,2,4]. This is worth 3 points because 1 > 0 [no points], 3 > 1 [no points], 0 <= 2 [one point], 2 <= 3 [one point], 4 <= 4 [one point].

Return the rotation index k that corresponds to the highest score we can achieve if we rotated nums by it. If there are multiple answers, return the smallest such index k.

Examples

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Example 1:

Input: nums = [2,3,1,4,0]
Output: 3
Explanation: Scores for each k are listed below:
k = 0, nums = [2,3,1,4,0], score 2
k = 1, nums = [3,1,4,0,2], score 3
k = 2, nums = [1,4,0,2,3], score 3
k = 3, nums = [4,0,2,3,1], score 4
k = 4, nums = [0,2,3,1,4], score 3
So we should choose k = 3, which has the highest score.

Example 2:

Input: nums = [1,3,0,2,4]
Output: 0
Explanation: nums will always have 3 points no matter how it shifts.
So we will choose the smallest k, which is 0.

Constraints

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• 1 <= nums.length <= 105
• 0 <= nums[i] < nums.length

Solution

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class Solution {
public:
  int bestRotation(vector<int>& nums) {
    vector<int> points(2 * nums.size() + 1, 0);
    int k = 0;
    int pMax = 0;

    for (int i = 0; i < nums.size(); i += 1) {
      if (nums[i] <= i) {
        points[0] += 1;
        points[(i - nums[i]) + 1] -= 1;
      }
                
      points[i + 1] += 1;
      points[i + (nums.size() - nums[i]) + 1] -= 1;
    }

    pMax = points[0];
    for (int i = 1; i < points.size(); i += 1) {
      points[i] += points[i - 1];
        if (points[i] > pMax) {
          pMax = points[i];
          k = i;
        }
      }
    return k;
  }   
};