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]] 思路：使用递归，循环尝试每一种可能
public class Solution { private static List<List<Integer>> res; public List<List<Integer>> combinationSum3(int k, int n) { res = new ArrayList<List<Integer>>(); if (k < 1 || n < 1) return res; List<Integer> solution = new ArrayList<Integer>(); findSolution(k, n, 0, solution, 1); return res; } private static void findSolution(int k, int n, int sum, List<Integer> solution, int pre) { if (sum == n && k == 0) { res.add(new ArrayList<Integer>(solution)); } else if (sum > n || k <= 0) { return; } for (int i = pre; i <= 9; i++) { solution.add(i); findSolution(k - 1, n, sum + i, solution, i + 1); solution.remove(solution.size() - 1); } } }
