再战leetcode (77. 组合)

class Solution {
    private List> res = new ArrayList>();

    public List> combine(int n, int k) {
        List path = new ArrayList<>();
        dfs(1, n, k, path, 0);
        return res;
    }

    public void dfs(int startIndex, int n, int k, List path, int depth) {
        if (depth == k) {
            List tempPath = new ArrayList<>(path);
            res.add(tempPath);
            return;
        }
        for (int i = startIndex; i <= n; i++) {
            path.add(i);
            dfs(i + 1, n, k, path, depth + 1);
            path.remove(path.size() - 1);
        }

    }
}