LC 846. Hand of Straights

Alice has a hand of cards, given as an array of integers.

Now she wants to rearrange the cards into groups so that each group is size W, and consists of Wconsecutive cards.

Return true if and only if she can.

 

Example 1:

Input: hand = [1,2,3,6,2,3,4,7,8], W = 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], W = 4
Output: false
Explanation: Alice's hand can't be rearranged into groups of 4.

Note:

1. 1 <= hand.length <= 10000
2. 0 <= hand[i] <= 10^9
3. 1 <= W <= hand.length

Runtime: 80 ms, faster than 24.90% of C++ online submissions for Hand of Straights.

我的思路很直接，用map保存。

class Solution {
public:
  bool isNStraightHand(vector<int>& hand, int W) {
        int n = hand.size();
        if (n < 1 || W < 1 || n < W)
        {
            return false;
        }
       
        if (n % W != 0)
        {
            return false;
        }
    map<int,int> mp;
    for(auto x : hand) mp[x]++;
    for(auto it : mp){
      if(it.second == 0) continue;
      int cntit = it.second;
      for(int i=1; i<W;i++){
        if(!mp.count(it.first) || mp[it.first+i] < mp[it.first]) return false;
        mp[it.first+i] -= mp[it.first];
      }
      mp[it.first] = 0;
    }
    for(auto it : mp){
      if(it.second != 0) return false;
    }
    return true;
  }
};

网上看到一个比较好的思路是，把所有的数%W，因为是连续的，所以一个连续的W个数modW后必定在0 ~ W-1 中是连续存在的，妙。

class Solution {
public:
    bool isNStraightHand(vector<int>& hand, int W) {
        int n = hand.size();
        if (n < 1 || W < 1 || n < W)
        {
            return false;
        }
       
        if (n % W != 0)
        {
            return false;
        }
        
        vector<int> count (W, 0);
        for (const int& h : hand)
        {
            ++count[h % W];
        }
        
        int expect = count.front();
        for(const int& c : count)
        {
            if (c != expect)
            {
                return false;
            }
        }
        
        return true;
    }
};