77. 组合

Author: w2xi

README.md

@@ -39,6 +39,7 @@
 |70|[爬楼梯](https://leetcode.cn/problems/climbing-stairs/)|[JavaScript](./algorithms/climbing-stairs.js)|Easy|
 |71|[简化路径](https://leetcode.cn/problems/simplify-path/)|[JavaScript](./algorithms/simplify-path.js)|Medium|
 |73|[矩阵置零](https://leetcode.cn/problems/set-matrix-zeroes/)|[JavaScript](./algorithms/set-matrix-zeroes.js)|Medium|
+|77|[组合](https://leetcode.cn/problems/combinations/)|[JavaScript](./algorithms/combinations.js)|Medium|
 |82|[删除排序链表中的重复元素 II](https://leetcode.cn/problems/remove-duplicates-from-sorted-list-ii/)|[JavaScript](./algorithms/remove-duplicates-from-sorted-list-ii.js)|Medium|
 |83|[删除排序链表中的重复元素](https://leetcode.cn/problems/remove-duplicates-from-sorted-list/)|[JavaScript](./algorithms/remove-duplicates-from-sorted-list.js)|Easy|
 |88|[合并两个有序数组](https://leetcode.cn/problems/merge-sorted-array/)|[JavaScript](./algorithms/merge-sorted-array.js)|Easy|

algorithms/combinations.js

@@ -0,0 +1,24 @@
+/**
+ * @param {number} n
+ * @param {number} k
+ * @return {number[][]}
+ */
+var combine = function (n, k) {
+  const result = [];
+  const path = [];
+  const backTracking = (n, k, startIndex) => {
+    // 终止条件
+    if (path.length === k) {
+      result.push(path.slice());
+      return;
+    }
+    for (let i = startIndex; i <= n; i++) { // 控制树的横向遍历
+      path.push(i);                         // 处理节点
+      backTracking(n, k, i + 1);            // 递归,控制树的纵向遍历,注意下一层搜索要从i+1开始
+      path.pop();                           // 回溯,撤销处理的节点
+    }
+  };
+  backTracking(n, k, 1);
+
+  return result;
+};