Create 22. Factor Combinations.py

12_Backtracking/22. Factor Combinations.py

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+# https://www.lintcode.com/problem/1308
+
+
+from typing import List
+
+class Solution:
+    def get_factors(self, n: int) -> List[List[int]]:
+        if n <= 1: 
+            return []
+
+        res = []
+        i = 2
+        while i*i <= n:
+            if n%i == 0:
+                res.append([i, n//i])
+                subres = self.get_factors(n//i)
+                for arr in subres:
+                    if arr[0] >= i:
+                        res.append([i] + arr)
+            i += 1
+
+        return res 
+
+
+# Time: O(sqrt(n) * log(n))    # https://algo.monster/liteproblems/254
+# Space: O(m + log(n))         where m is the number of combinations of factors.