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Algorithms

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

You may return the answer in any order.

&nbsp;
Example 1:

<pre>
Input: n = 4, k = 2
Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
Explanation: There are 4 choose 2 = 6 total combinations.
Note that combinations are unordered, i.e., [1,2] and [2,1] are considered to be the same combination.
</pre>

Example 2:

<pre>
Input: n = 1, k = 1
Output: [[1]]
Explanation: There is 1 choose 1 = 1 total combination.
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= n &lt;= 20</code></li>
	<li><code>1 &lt;= k &lt;= n</code></li>
</ul>

combine

Combinations

Combination Sum

combination-sum

组合总和

Permutations

permutations

全排列

Backtracking

给定两个整数 <code>n</code> 和 <code>k</code>，返回范围 <code>[1, n]</code> 中所有可能的 <code>k</code> 个数的组合。

你可以按 任何顺序 返回答案。

 

示例 1：

<pre>
输入：n = 4, k = 2
输出：
[
 [2,4],
 [3,4],
 [2,3],
 [1,2],
 [1,3],
 [1,4],
]</pre>

示例 2：

<pre>
输入：n = 1, k = 1
输出：[[1]]</pre>

 

提示：

<ul>
	<li><code>1 <= n <= 20</code></li>
	<li><code>1 <= k <= n</code></li>
</ul>