Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.
For example,
If n = 4 and k = 2, a solution is:
[
[2,4],
[3,4],
[2,3],
[1,2],
[1,3],
[1,4],
]
題意：給你n個(gè)數(shù)声旺，組成k位的密碼昔逗，列出所有可能。
思路：遞歸，動(dòng)態(tài)往里添加
代碼：
class Solution {
public List<List<Integer>> combine(int n, int k) {
List<List<Integer>> res = new ArrayList<>();
fun(res, new ArrayList<Integer>(), 0, n, k);
return res;
}
public void fun(List<List<Integer>> res, List<Integer> list, int start, int n, int k) {
if (list.size() == k) {
res.add(new ArrayList<Integer>(list));
return;
}
for (int i = start; i < n; i++) {
list.add(i + 1);
fun(res, list, i + 1, n, k);
list.remove(list.size() - 1);
}
}
}
