题目分类

77. Combinations

Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].

You may return the answer in any order.

题目解析：

• 求组合可以使用回溯

代码：

class Solution {
    public List<List<Integer>> combine(int n, int k) {
        List<List<Integer>> combs = new ArrayList<>();
        backtracking(n, k, 1, new ArrayList<>(), combs);
        return combs;
    }

    public void backtracking(int n, int k, int idx, List<Integer> path, List<List<Integer>> combs) {
        if (path.size() == k) {
            combs.add(new ArrayList<>(path));
            return;
        }
        for (int i = idx; i <= n; i++) {
            path.add(i);
            backtracking(n, k, i+1, path, combs);
            path.remove(path.size() - 1);
        }
    }
}