659. Split Array into Consecutive Subsequences!

class Solution {
    public boolean isPossible(int[] nums) {
        // deal with the number depending on conditions
        
        // record the frequency of num in nums
        Map<Integer, Integer> freq = new HashMap<>();
        Map<Integer, Integer> need = new HashMap<>();
        
        for(int num : nums) freq.put(num, freq.getOrDefault(num, 0)+1);
        
        for(int num : nums){
            if(freq.get(num)==0) continue;
            //first check if the num can be append to existing subsequence,
            //if not, then check if num can form a subsequence,
            //start from num
            if(need.containsKey(num) && need.get(num) >0){
                need.put(num, need.get(num)-1);
                freq.put(num, freq.get(num)-1);
                need.put(num+1, need.getOrDefault(num+1,0)+1);
            }else if(freq.getOrDefault(num, 0)>0 
                     && freq.getOrDefault(num+1, 0)>0
                     && freq.getOrDefault(num+2, 0)>0){
                freq.put(num, freq.get(num)-1);
                freq.put(num+1, freq.get(num+1)-1);
                freq.put(num+2, freq.get(num+2)-1);
                need.put(num+3, need.getOrDefault(num+3,0)+1);
            }else{
                return false;
            }
        }
        return true;
    }
}