$ cat ./coding/216-combination-sum-iii.md

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216. Combination Sum III

這一題和 77. Combinations 與 39. Combination Sum 差不多，其實比 40. Combination II 簡單。

class Solution:
    def combinationSum3(self, k: int, n: int) -> List[List[int]]:
        ans = []
        def backtrack(curr, target, start):
            if target == 0 and if len(curr) == k:
                ans.append(list(curr))
                return
            if target < 0:
                return
            else:
                for i in range(start, 10):
                    curr.append(i)
                    backtrack(curr, target - i, i + 1)
                    curr.pop()
        backtrack([], n, 1)
        return ans

class Solution:
    def combinationSum3(self, k: int, n: int) -> List[List[int]]:
        
        res = []
        
        def backtrack(curr, total, start):
            if len(curr) == k:
                if total == n:
                    res.append(curr.copy())
                return
            if total > n:
                return
            
            for i in range(start, 10):
                curr.append(i)
                total += i
                backtrack(curr, total, i + 1)
                curr.pop()
                total -= i
        
        backtrack([], 0, 1)
    
        return res

$ ls ./coding/ | grep -v 216-combination-sum-iii