Add solution #673

Author: JoshCrozier

README.md

@@ -506,6 +506,7 @@
 670|[Maximum Swap](./0670-maximum-swap.js)|Medium|
 671|[Second Minimum Node In a Binary Tree](./0671-second-minimum-node-in-a-binary-tree.js)|Easy|
 672|[Bulb Switcher II](./0672-bulb-switcher-ii.js)|Medium|
+673|[Number of Longest Increasing Subsequence](./0673-number-of-longest-increasing-subsequence.js)|Medium|
 680|[Valid Palindrome II](./0680-valid-palindrome-ii.js)|Easy|
 684|[Redundant Connection](./0684-redundant-connection.js)|Medium|
 686|[Repeated String Match](./0686-repeated-string-match.js)|Easy|

solutions/0673-number-of-longest-increasing-subsequence.js

@@ -0,0 +1,36 @@
+/**
+ * 673. Number of Longest Increasing Subsequence
+ * https://leetcode.com/problems/number-of-longest-increasing-subsequence/
+ * Difficulty: Medium
+ *
+ * Given an integer array nums, return the number of longest increasing subsequences.
+ *
+ * Notice that the sequence has to be strictly increasing.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var findNumberOfLIS = function(nums) {
+  const lengths = new Array(nums.length).fill(1);
+  const counts = new Array(nums.length).fill(1);
+
+  for (let i = 1; i < nums.length; i++) {
+    for (let j = 0; j < i; j++) {
+      if (nums[i] > nums[j]) {
+        if (lengths[j] + 1 > lengths[i]) {
+          lengths[i] = lengths[j] + 1;
+          counts[i] = counts[j];
+        } else if (lengths[j] + 1 === lengths[i]) {
+          counts[i] += counts[j];
+        }
+      }
+    }
+  }
+
+  const max = Math.max(...lengths);
+  return lengths.reduce((sum, l, i) => {
+    return sum + (l === max ? counts[i] : 0);
+  }, 0);
+};