combination-sum

Author: wuduhren

problems/python3/combination-sum.py

@@ -0,0 +1,29 @@
+"""
+Time: O(N^K), assuming the number of element in the combination that sums up to "target" is K.
+For each element, there is N choices.
+Which means the number of combination is N*N*N... for K times.
+~= O(N^K)
+
+Space: O(K)
+
+K is approximate to target/min(candidates).
+"""
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        def helper(i, currSum, target):
+            if currSum>target:
+                return
+            
+            if currSum==target:
+                ans.append(combination.copy())
+                return
+            
+            for j in range(i, len(candidates)):
+                combination.append(candidates[j])
+                helper(j, currSum+candidates[j], target)
+                combination.pop()
+                
+        ans = []
+        combination = []
+        helper(0, 0, target)
+        return ans