Add solution #670

Author: JoshCrozier

README.md

@@ -502,6 +502,7 @@
 664|[Strange Printer](./0664-strange-printer.js)|Hard|
 667|[Beautiful Arrangement II](./0667-beautiful-arrangement-ii.js)|Medium|
 668|[Kth Smallest Number in Multiplication Table](./0668-kth-smallest-number-in-multiplication-table.js)|Hard|
+670|[Maximum Swap](./0670-maximum-swap.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/0670-maximum-swap.js

@@ -0,0 +1,31 @@
+/**
+ * 670. Maximum Swap
+ * https://leetcode.com/problems/maximum-swap/
+ * Difficulty: Medium
+ *
+ * You are given an integer num. You can swap two digits at most once to get the maximum
+ * valued number.
+ *
+ * Return the maximum valued number you can get.
+ */
+
+/**
+ * @param {number} num
+ * @return {number}
+ */
+var maximumSwap = function(num) {
+  const digits = [...(num).toString()];
+  const last = new Array(10).fill(-1);
+  digits.forEach((d, i) => last[d] = i);
+
+  for (let i = 0; i < digits.length; i++) {
+    for (let d = 9; d > digits[i]; d--) {
+      if (last[d] > i) {
+        [digits[i], digits[last[d]]] = [digits[last[d]], digits[i]];
+        return +digits.join('');
+      }
+    }
+  }
+
+  return num;
+};