Group the People Given the Group Size They Belong To

Description

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

Solution(javascript)

/**
 * @param {number[]} groupSizes
 * @return {number[][]}
 */
const groupThePeople = function (groupSizes = []) {
  const map = {}
  groupSizes.forEach((size, index) => {
    map[size] = map[size] || []
    const list = map[size]
    const lastIndex = list.length - 1
    if (list[lastIndex] && list[lastIndex].length < size) {
      list[lastIndex].push(index)
    } else {
      list.push([index])
    }
  })
  return Object.keys(map).reduce((acc, key) => {
    acc = acc.concat(map[key])
    return acc
  }, [])
}