Add solution #956

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,041 LeetCode solutions in JavaScript
+# 1,042 LeetCode solutions in JavaScript
 
 [https://leetcode.com/](https://leetcode.com/)
 
@@ -765,6 +765,7 @@
 953|[Verifying an Alien Dictionary](./solutions/0953-verifying-an-alien-dictionary.js)|Easy|
 954|[Array of Doubled Pairs](./solutions/0954-array-of-doubled-pairs.js)|Medium|
 955|[Delete Columns to Make Sorted II](./solutions/0955-delete-columns-to-make-sorted-ii.js)|Medium|
+956|[Tallest Billboard](./solutions/0956-tallest-billboard.js)|Hard|
 966|[Vowel Spellchecker](./solutions/0966-vowel-spellchecker.js)|Medium|
 970|[Powerful Integers](./solutions/0970-powerful-integers.js)|Easy|
 976|[Largest Perimeter Triangle](./solutions/0976-largest-perimeter-triangle.js)|Easy|

solutions/0956-tallest-billboard.js

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+/**
+ * 956. Tallest Billboard
+ * https://leetcode.com/problems/tallest-billboard/
+ * Difficulty: Hard
+ *
+ * You are installing a billboard and want it to have the largest height. The billboard will have
+ * two steel supports, one on each side. Each steel support must be an equal height.
+ *
+ * You are given a collection of rods that can be welded together. For example, if you have rods
+ * of lengths 1, 2, and 3, you can weld them together to make a support of length 6.
+ *
+ * Return the largest possible height of your billboard installation. If you cannot support the
+ * billboard, return 0.
+ */
+
+/**
+ * @param {number[]} rods
+ * @return {number}
+ */
+var tallestBillboard = function(rods) {
+  const differences = new Map([[0, 0]]);
+
+  for (const rod of rods) {
+    const currentDiffs = new Map(differences);
+
+    for (const [diff, taller] of currentDiffs) {
+      const shorter = taller - diff;
+      const newDiff = diff + rod;
+      const newTaller = taller + rod;
+      differences.set(newDiff, Math.max(differences.get(newDiff) || 0, newTaller));
+
+      const diffAbs = Math.abs(diff - rod);
+      const diffMax = Math.max(shorter + rod, taller);
+      differences.set(diffAbs, Math.max(differences.get(diffAbs) || 0, diffMax));
+    }
+  }
+
+  return differences.get(0) || 0;
+};