216. Combination Sum III

Difficulty: Medium
18 / 18 test cases passed.
Runtime: 32 ms
Memory Usage: 13.8 MB

Author: YuriSpiridonov

Medium/216.CombinationSumIII.py

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+"""
+    Find all possible combinations of k numbers that add up to a number n, 
+    given that only numbers from 1 to 9 can be used and each combination should 
+    be a unique set of numbers.
+
+    Note:
+        - All numbers will be positive integers.
+        - The solution set must not contain duplicate combinations.
+
+    Example:
+    Input: k = 3, n = 7
+    Output: [[1,2,4]]
+
+    Example:
+    Input: k = 3, n = 9
+    Output: [[1,2,6], [1,3,5], [2,3,4]]
+"""
+#Difficulty: Medium
+#18 / 18 test cases passed.
+#Runtime: 32 ms
+#Memory Usage: 13.8 MB
+
+#Runtime: 32 ms, faster than 68.72% of Python3 online submissions for Combination Sum III.
+#Memory Usage: 13.8 MB, less than 62.64% of Python3 online submissions for Combination Sum III.
+
+class Solution:
+    def combinationSum3(self, k: int, n: int) -> List[List[int]]:
+        if k > n:
+            return
+        self.result = []
+        self.backtracking(k, n)
+        return self.result
+
+    def backtracking(self, k, n, start = 1, summ = 0, count = 0, nums = []):
+        if count > k:
+            return
+        if count == k and summ == n:
+            result = []
+            result.extend(nums)
+            self.result.append(result)
+            return
+        for num in range(start, 10):
+            if summ + num > n:
+                break
+            nums.append(num)
+            self.backtracking(k, n, num+1, summ+num, count+1, nums)
+            nums.pop()