77. 组合

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台

解题思路：纵向遍历，遇到叶子节点返回上一节点

java：

class Solution {List<List<Integer>> result = new ArrayList<>();LinkedList<Integer> path = new LinkedList<>();public List<List<Integer>> combine(int n, int k) {combineHelper(n, k, 1);return result;}private void combineHelper(int n, int k, int startIndex){if (path.size() == k){result.add(new ArrayList<>(path));return;}for (int i = startIndex; i <= n - (k - path.size()) + 1; i++){path.add(i);combineHelper(n, k, i + 1);path.removeLast();}}
}