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Candy⚓︎

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Description⚓︎

There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings.

You are giving candies to these children subjected to the following requirements:

  • Each child must have at least one candy.
  • Children with a higher rating get more candies than their neighbors.

Return the minimum number of candies you need to have to distribute the candies to the children.

Example 1:

  • Input: ratings = [1,0,2]
  • Output: 5
  • Explanation: You can allocate to the first, second and third child with 2, 1, 2 candies respectively.

Example 2:

  • Input: ratings = [1,2,2]
  • Output: 4
  • Explanation: You can allocate to the first, second and third child with 1, 2, 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions.

Constraints:

  • n == ratings.length
  • 1 <= n <= 2 * 10^4
  • 0 <= ratings[i] <= 2 * 10^4

Solution⚓︎

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class Solution {
public:
    int candy(vector<int>& ratings) {
        int n = ratings.size();
        vector<int> candies(n, 1);
        for (int i = 1; i < n; i++) {
            if (ratings[i] > ratings[i - 1])
                candies[i] = candies[i - 1] + 1;
        }
        for (int i = n - 2; i >= 0; i--) {
            if (ratings[i] > ratings[i + 1])
                candies[i] = max(candies[i], candies[i + 1] + 1);
        }
        return accumulate(candies.begin(), candies.end(), 0);
    }
};
  • Time complexity: \(O(n)\);
  • Space complexity: \(O(n)\).