Combination

The brutal-force way to calculate all the combination.

Linkage

https://leetcode.com/problems/combinations/description/

Code

class Solution:
    def combine(self, n, k):
        """
        :type n: int
        :type k: int
        :rtype: List[List[int]]
        """
        ret = []
        self.add(ret, 1, n, [], k) 
        return ret
            
    def add(self, ret, start, end, item, residual):
        if residual == 0:
            ret.append(item)
            return 
        
        for i in range(start, end-residual+2):
            new_item = item[:]
            new_item.append(i)
            self.add(ret, i+1, end, new_item, residual-1)