# Leetcode 1282. Group the People Given the Group Size They Belong To

2 min readJan 21, 2022

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[medium]

There are `n` people that are split into some unknown number of groups. Each person is labeled with a unique ID from `0` to `n - 1`.

You are given an integer array `groupSizes`, where `groupSizes[i]` is the size of the group that person `i` is in. For example, if `groupSizes[1] = 3`, then person `1` must be in a group of size `3`.

Return a list of groups such that each person `i` is in a group of size `groupSizes[i]`.

Each person should appear in exactly one group, and every person must be in a group. If there are multiple answers, return any of them. It is guaranteed that there will be at least one valid solution for the given input.

Example 1:

`Input: groupSizes = [3,3,3,3,3,1,3]Output: [[5],[0,1,2],[3,4,6]]Explanation: The first group is [5]. The size is 1, and groupSizes[5] = 1.The second group is [0,1,2]. The size is 3, and groupSizes[0] = groupSizes[1] = groupSizes[2] = 3.The third group is [3,4,6]. The size is 3, and groupSizes[3] = groupSizes[4] = groupSizes[6] = 3.Other possible solutions are [[2,1,6],[5],[0,4,3]] and [[5],[0,6,2],[4,3,1]].`

Example 2:

`Input: groupSizes = [2,1,3,3,3,2]Output: [[1],[0,5],[2,3,4]]`

Constraints:

• `groupSizes.length == n`
• `1 <= n <= 500`
• `1 <= groupSizes[i] <= n`

[Think]

1. create a map, and put same group size people into the list
2. if list size match the group size number, add it into the result list, and remove the list from map
3. In this answer, it had at least one answer, so no need to worry if anyone didn’t join the group
4. We could know that after the end of loop, the map should be empty

[Java]

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CS new grad, 6 years experience related to supply chain management. Located in Bay area