https://leetcode.com/problems/combination-sum-iii/
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.
Ensure that numbers within the set are sorted in ascending order.
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]]
解题思路：
新题，与前面的系列相比，简单了一些，常规的dfs，没有啥好说的。
public class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
List<Integer> cur = new ArrayList<Integer>();
dfs(k, n, res, cur, 1, 0);
return res;
}
public void dfs(int k, int n, List<List<Integer>> res, List<Integer> cur, int step, int sum) {
if(cur.size() == k && sum == n) {
res.add(new ArrayList(cur));
return;
}
if(cur.size() > k) {
return;
}
if(cur.size() <= k && sum > n) {
return;
}
for(int i = step; i < 10; i++) {
cur.add(i);
sum += i;
dfs(k, n, res, cur, i + 1, sum);
cur.remove(cur.size() - 1);
sum -= i;
}
}
}
//20181013
class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
List<Integer> cur = new ArrayList<Integer>();
dfs(res, cur, k, n, 1, 0);
return res;
}
public void dfs(List<List<Integer>> res, List<Integer> cur, int k, int n, int start, int sum) {
if (cur.size() == k && sum == n) {
res.add(new ArrayList(cur));
}
for (int i = start; i <= Math.min(n, 9); i++) {
cur.add(i);
dfs(res, cur, k, n, i + 1, sum + i);
cur.remove(cur.size() - 1);
}
}
}