Update 1955-count-number-of-special-subsequences.js

Author: everthis

1955-count-number-of-special-subsequences.js

@@ -1,3 +1,25 @@
+/*
+ * @lc app=leetcode id=1955 lang=javascript
+ *
+ * [1955] Count Number of Special Subsequences
+ */
+
+// @lc code=start
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+const countSpecialSubsequences = function (nums) {
+  const dp = Array(3).fill(0),
+    mod = 10 ** 9 + 7
+  for (let e of nums) {
+    dp[e] = (((dp[e] + dp[e]) % mod) + (e > 0 ? dp[e - 1] : 1)) % mod
+  }
+  return dp[2]
+}
+
+// another
+
 /**
  * @param {number[]} nums
  * @return {number}