27. Candy.cpp

/*
Candy
=====

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 * 104
0 <= ratings[i] <= 2 * 104
*/

class Solution
{
public:
  int candy(vector<int> &A)
  {
    int n = A.size(), ans = 0;
    vector<int> candies(n, 1);

    for (int i = 1; i < n; ++i)
    {
      if (A[i] > A[i - 1])
        candies[i] = 1 + candies[i - 1];
    }

    for (int i = n - 2; i >= 0; --i)
    {
      if (A[i] > A[i + 1])
        candies[i] = max(candies[i], candies[i + 1] + 1);
    }

    for (auto &i : candies)
      ans += i;
    return ans;
  }
};