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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.
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]]
Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.
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1 public class Solution { 2 public List<List<Integer>> combinationSum3(int k, int n) { 3 ArrayList<List<Integer>> ans = new ArrayList<List<Integer>>(); 4 ArrayList<Integer> tmp = new ArrayList<Integer>(); 5 if(k < 1 || n < 1) return ans; 6 combinationDFS(ans, tmp, k, n, 1, 0); 7 return ans; 8 } 9 10 public void combinationDFS(ArrayList<List<Integer>> ans, ArrayList<Integer> tmp, int k, int n, int level, int sum){ 11 if(sum == n && k == 0){ 12 ans.add(new ArrayList(tmp)); 13 return; 14 }else if(sum > n || k < 0){ 15 return; 16 } 17 for(int i = level; i<=9; i++){ 18 tmp.add(i); 19 combinationDFS(ans,tmp,k-1,n,i+1,sum+i); 20 tmp.remove(tmp.size()-1); 21 } 22 } 23 }
216. Combination Sum III java solutions
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原文地址：http://www.cnblogs.com/guoguolan/p/5613797.html
