dfs: 组合

Change-Id: Ib9e0541639054882b8121210e76e99d253c3f71b

Author: qieguo2016

go/leetcode/77.组合.go

@@ -0,0 +1,53 @@
+/*
+ * @lc app=leetcode.cn id=77 lang=golang
+ *
+ * [77] 组合
+ *
+ * https://leetcode-cn.com/problems/combinations/description/
+ *
+ * algorithms
+ * Medium (68.47%)
+ * Likes:    125
+ * Dislikes: 0
+ * Total Accepted:    12.8K
+ * Total Submissions: 18.6K
+ * Testcase Example:  '4\n2'
+ *
+ * 给定两个整数 n 和 k，返回 1 ... n 中所有可能的 k 个数的组合。
+ * 
+ * 示例:
+ * 
+ * 输入: n = 4, k = 2
+ * 输出:
+ * [
+ * ⁠ [2,4],
+ * ⁠ [3,4],
+ * ⁠ [2,3],
+ * ⁠ [1,2],
+ * ⁠ [1,3],
+ * ⁠ [1,4],
+ * ]
+ * 
+ */
+
+// @lc code=start
+func combine(n int, k int) [][]int {
+	out := []int{}
+	res := [][]int{}
+	dfs(n, k, &out, &res)
+	return res
+}
+
+func dfs(n int, k int, out *[]int, res *[][]int) {
+	if k <= 0 {
+		*res = append(*res, append([]int{}, (*out)...))
+		return
+	}
+	for i := n; i > 0; i-- {
+		*out = append(*out, i)
+		dfs(i-1, k-1, out, res)
+		*out = (*out)[:len(*out)-1]
+	}
+}
+// @lc code=end
+