add subsets script.

Author: everthis

78-subsets.js

@@ -0,0 +1,23 @@
+/**
+ * @param {number[]} nums
+ * @return {number[][]}
+ */
+
+function subsets(nums) {
+  const list = [];
+  const len = nums.length;
+  const subsetNum = Math.pow(2, len);
+  for (let n = 0; n < subsetNum; n++) {
+    list[n] = [];
+  }
+  for (let i = 0; i < len; i++) {
+    for (let j = 0; j < subsetNum; j++) {
+      if ((j >> i) & 1) {
+        list[j].push(nums[i]);
+      }
+    }
+  }
+  return list;
+}
+
+console.log(subsets([1, 2, 3]));