Add solution #399

Author: JoshCrozier

README.md

@@ -244,6 +244,7 @@
 392|[Is Subsequence](./0392-is-subsequence.js)|Easy|
 394|[Decode String](./0394-decode-string.js)|Medium|
 395|[Longest Substring with At Least K Repeating Characters](./0395-longest-substring-with-at-least-k-repeating-characters.js)|Medium|
+399|[Evaluate Division](./0399-evaluate-division.js)|Medium|
 405|[Convert a Number to Hexadecimal](./0405-convert-a-number-to-hexadecimal.js)|Easy|
 407|[Trapping Rain Water II](./0407-trapping-rain-water-ii.js)|Hard|
 412|[Fizz Buzz](./0412-fizz-buzz.js)|Easy|

solutions/0399-evaluate-division.js

@@ -0,0 +1,49 @@
+/**
+ * 399. Evaluate Division
+ * https://leetcode.com/problems/evaluate-division/
+ * Difficulty: Medium
+ *
+ * You are given an array of variable pairs equations and an array of real numbers values,
+ * where equations[i] = [Ai, Bi] and values[i] represent the equation Ai / Bi = values[i].
+ * Each Ai or Bi is a string that represents a single variable.
+ *
+ * You are also given some queries, where queries[j] = [Cj, Dj] represents the jth query
+ * where you must find the answer for Cj / Dj = ?.
+ *
+ * Return the answers to all queries. If a single answer cannot be determined, return -1.0.
+ *
+ * Note: The input is always valid. You may assume that evaluating the queries will not
+ * result in division by zero and that there is no contradiction.
+ *
+ * Note: The variables that do not occur in the list of equations are undefined, so the
+ * answer cannot be determined for them.
+ */
+
+/**
+ * @param {string[][]} equations
+ * @param {number[]} values
+ * @param {string[][]} queries
+ * @return {number[]}
+ */
+var calcEquation = function(equations, values, queries) {
+  const map = equations.reduce((result, [a, b], index) => {
+    result.set(a, [...(result.get(a) ?? []), [b, values[index]]]);
+    result.set(b, [...(result.get(b) ?? []), [a, 1 / values[index]]]);
+    return result;
+  }, new Map());
+
+  function traverse([a, b], seen = new Set(), current = 1) {
+    if (!map.has(a) || !map.has(b)) return -1;
+    if (a === b) return current;
+    seen.add(a);
+
+    for (const [key, value] of map.get(a)) {
+      if (seen.has(key)) continue;
+      const result = traverse([key, b], seen, current * value);
+      if (result) return result;
+    }
+    return null;
+  }
+
+  return queries.map(item => traverse(item) ?? -1);
+};