Add solution #859

Author: JoshCrozier

README.md

@@ -666,6 +666,7 @@
 856|[Score of Parentheses](./0856-score-of-parentheses.js)|Medium|
 857|[Minimum Cost to Hire K Workers](./0857-minimum-cost-to-hire-k-workers.js)|Hard|
 858|[Mirror Reflection](./0858-mirror-reflection.js)|Medium|
+859|[Buddy Strings](./0859-buddy-strings.js)|Easy|
 867|[Transpose Matrix](./0867-transpose-matrix.js)|Easy|
 868|[Binary Gap](./0868-binary-gap.js)|Easy|
 872|[Leaf-Similar Trees](./0872-leaf-similar-trees.js)|Easy|

solutions/0859-buddy-strings.js

@@ -0,0 +1,41 @@
+/**
+ * 859. Buddy Strings
+ * https://leetcode.com/problems/buddy-strings/
+ * Difficulty: Easy
+ *
+ * Given two strings s and goal, return true if you can swap two letters in s so the result is
+ * equal to goal, otherwise, return false.
+ *
+ * Swapping letters is defined as taking two indices i and j (0-indexed) such that i != j and
+ * swapping the characters at s[i] and s[j].
+ *
+ * For example, swapping at indices 0 and 2 in "abcd" results in "cbad".
+ */
+
+/**
+ * @param {string} s
+ * @param {string} goal
+ * @return {boolean}
+ */
+var buddyStrings = function(s, goal) {
+  if (s.length !== goal.length) return false;
+
+  const differences = [];
+  const charCount = new Map();
+  let hasDuplicate = false;
+
+  for (let i = 0; i < s.length; i++) {
+    if (s[i] !== goal[i]) {
+      differences.push(i);
+      if (differences.length > 2) return false;
+    }
+    charCount.set(s[i], (charCount.get(s[i]) || 0) + 1);
+    if (charCount.get(s[i]) > 1) hasDuplicate = true;
+  }
+
+  if (differences.length === 0) return hasDuplicate;
+  if (differences.length !== 2) return false;
+
+  const [first, second] = differences;
+  return s[first] === goal[second] && s[second] === goal[first];
+};