135. Candy

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135. Candy

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:

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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:

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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

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    int candy(vector<int>& ratings) {
        vector<int> left2right(ratings.size(), 1);
        vector<int> right2left(ratings.size(), 1);
        for (int i = 1; i < ratings.size(); i++) {
            if (ratings[i] > ratings[i - 1]) {
                left2right[i] = left2right[i - 1] + 1;
            }
        }
        for (int i = ratings.size() - 2; i >= 0; i--) {
            if (ratings[i] > ratings[i + 1]) {
                right2left[i] = right2left[i + 1] + 1;
            }
        }
        int res = 0;
        for (int i = 0; i < ratings.size(); i++) {
            res += max(left2right[i], right2left[i]);
        }
        return res;
    }
};