659. Split Array into Consecutive Subsequences

You are given an integer array nums that is sorted in non-decreasing order.

Determine if it is possible to split nums into one or more subsequences such that both of the following conditions are true:

• Each subsequence is a consecutive increasing sequence (i.e. each integer is exactly one more than the previous integer).
• All subsequences have a length of 3 or more.
  Return true if you can split nums according to the above conditions, or false otherwise.

A subsequence of an array is a new array that is formed from the original array by deleting some (can be none) of the elements without disturbing the relative positions of the remaining elements. (i.e., [1,3,5] is a subsequence of [1,2,3,4,5] while [1,3,2] is not).

class Solution {
    map<int, int> count;
    unordered_map<int, int> end;
public:
    bool isPossible(vector<int>& nums) {
        for(auto n : nums) count[n]++;
        for(auto n : nums) {
            if(!count[n]) continue;
            count[n]--;
            
            if(end[n-1] > 0) {
                end[n-1]--;
                end[n]++;
            }else if(count[n + 1] > 0 and count[n + 2] > 0) {
                count[n+1]--;
                count[n+2]--;
                end[n+2]++;
            } else return false;
        }
        return true;
    }
};