> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Candy Python Solution with Tests

> Tested Python solution for LeetCode 135 with 18 pytest cases. Generate a practice environment with lcpy.

LeetCode 135, Hard. Topics: Array, Greedy. [View on LeetCode](https://leetcode.com/problems/candy/description/).

Generate this problem as a practice environment: tested reference solution, 18 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 135   # by problem number
lcpy gen -s candy   # by problem name
```

## Problem

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*.

### Examples

```
Input: ratings = [1,0,2]
Output: 5
```

**Explanation:** You can allocate to the first, second and third child with 2, 1, 2 candies respectively.

```
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

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/candy/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/candy/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(n)
    # Space: O(n)
    def candy(self, ratings: list[int]) -> int:
        n = len(ratings)
        candies = [1] * n

        # Left-to-right: satisfy higher-than-left-neighbor constraint
        for i in range(1, n):
            if ratings[i] > ratings[i - 1]:
                candies[i] = candies[i - 1] + 1

        # Right-to-left: satisfy higher-than-right-neighbor constraint
        for i in range(n - 2, -1, -1):
            if ratings[i] > ratings[i + 1]:
                candies[i] = max(candies[i], candies[i + 1] + 1)

        return sum(candies)
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(n) | O(n)  |

## Tags

[NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).