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/

Code

Time Complexity: $O(n\log n)$, Space Complexity: $O(n)$

注意在 iterate through map 時，要確保 if(value > 0)。

這題的概念類似 Longest Consecutive Sequence

class Solution {
public:
    bool isNStraightHand(vector<int>& hand, int groupSize) {
        if(hand.size() % groupSize != 0) return false;
        map<int, int> mp;
        for(auto h: hand) {
            mp[h]++;
        }
 
        for(auto [key, value]: mp) {
            auto tmp = key;
            if(value > 0) {
                for(int i = 0; i < groupSize; i++) {
                    if(mp.find(tmp) == mp.end())
                        return false;
                    mp[tmp] -= value;
 
                    if(mp[tmp] < 0)
                        return false;
                    tmp++;
                }
            }
        }
 
        return true;
    }
};

Source

• Hand of Straights - LeetCode