LeetCode 846. Hand of Straights

原题链接在这里：https://leetcode.com/problems/hand-of-straights/

题目：

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 W consecutive 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

题解：

Get the smallest number, check if there are next W consecutive numbers.

Have a TreeMap map to maintain the frequency of each number.

Every time, get the latest number key in map and its count, for next key + 1, key +2 ... key + W -1, if their frequency < count, then they can't be made as W consecutive cards, return false.

Otherwise, remove the count from each of their frequency.

Time Complexity: O(mwlogm). TreeMap, get, put, remove all takes O(logm). m = hand.length.

Space: O(m).

AC Java:  

class Solution {
    public boolean isNStraightHand(int[] hand, int W) {
        TreeMap<Integer, Integer> map = new TreeMap<>();
        for(int i : hand){
            map.put(i, map.getOrDefault(i, 0)+1);
        }
        
        for(int key : map.keySet()){
            int count = map.get(key);
            if(count > 0){
                for(int i = key+W-1; i>=key; i--){
                    if(map.getOrDefault(i, 0) < count){
                        return false;
                    }
                    
                    map.put(i, map.get(i)-count);
                }
            }
        }
        
        return true;
    }
}