Question Definition
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.
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]]
My Java Solution
class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> result = new LinkedList<>();
List<Integer> cur = new LinkedList<>();
dfs(k, n, 1, cur, result);
return result;
}
private void dfs(int k, int n, int start, List<Integer> cur, List<List<Integer>> result){
if(k < 0 || n < 0 || (k == 1 && n > 9)) return;
if(k == 0 && n == 0) {
result.add(new LinkedList<>(cur));
return;
}
for(int i = start; i <= 9; i++){
cur.add(i);
dfs(k - 1, n - i, i + 1, cur, result);
cur.remove(cur.size() - 1);
}
}
}
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