leetcode_gym/_problems/combinationSum3.md

layout, title, last_solved, category, leetcode_url, status

layout	title	last_solved	category	leetcode_url	status
page	Combination Sum III		backtrack	https://leetcode.com/problems/combination-sum-iii	Attempted

Problem

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:

The solution set must not contain duplicate combinations.
 

Example 1:

Input: k = 3, n = 7
Output: [[1,2,4]]
Example 2:

Input: k = 3, n = 9
Output: [[1,2,6],[1,3,5],[2,3,4]]
Example 3:

Input: k = 4, n = 1
Output: []
Example 4:

Input: k = 3, n = 2
Output: []
Example 5:

Input: k = 9, n = 45
Output: [[1,2,3,4,5,6,7,8,9]]

Solution

{% highlight python %}

def combinationSum3(self, k: int, n: int) -> List[List[int]]:
    
    
    output = []
    
    def backtrack(output, current, num, sumsofar):
        
        if len(current)==k and sumsofar==n:
            output.append(current.copy())
            return
        
        for i in range(num, 10):
            if sumsofar+1 > n: break
            backtrack(output, current+[i], i+1, sumsofar+i)
            
    
    
    backtrack(output, [], 1, 0)
    return output

{% endhighlight %}

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{% highlight python %}

{% endhighlight %}