846. Hand of Straights

Description

Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize, and consists of groupSize consecutive cards.

Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize, return true if she can rearrange the cards, or false otherwise.

 

Example 1:

Input: hand = [1,2,3,6,2,3,4,7,8], groupSize = 3
Output: true
Explanation: Alice's hand can be rearranged as [1,2,3],[2,3,4],[6,7,8]

Example 2:

Input: hand = [1,2,3,4,5], groupSize = 4
Output: false
Explanation: Alice's hand can not be rearranged into groups of 4.

 

Constraints:

• 1 <= hand.length <= 104
• 0 <= hand[i] <= 109
• 1 <= groupSize <= hand.length

 

Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/

 

Solutions

Solution: Greedy

• Time complexity: O(nlogn)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {number[]} hand
 * @param {number} groupSize
 * @return {boolean}
 */
const isNStraightHand = function (hand, groupSize) {
  const n = hand.length;

  if (n % groupSize) return false;
  hand.sort((a, b) => a - b);

  const cardMap = hand.reduce((map, card) => {
    const count = map.get(card) ?? 0;

    return map.set(card, count + 1);
  }, new Map());

  for (const [card, count] of cardMap) {
    if (!count) continue;

    for (let current = card + 1; current < card + groupSize; current++) {
      const currentCount = cardMap.get(current) ?? 0;

      if (currentCount < count) return false;
      cardMap.set(current, currentCount - count);
    }
  }
  return true;
};