Add solution #777

Author: JoshCrozier

README.md

@@ -587,6 +587,7 @@
 770|[Basic Calculator IV](./0770-basic-calculator-iv.js)|Hard|
 773|[Sliding Puzzle](./0773-sliding-puzzle.js)|Hard|
 775|[Global and Local Inversions](./0775-global-and-local-inversions.js)|Medium|
+777|[Swap Adjacent in LR String](./0777-swap-adjacent-in-lr-string.js)|Medium|
 783|[Minimum Distance Between BST Nodes](./0783-minimum-distance-between-bst-nodes.js)|Easy|
 784|[Letter Case Permutation](./0784-letter-case-permutation.js)|Medium|
 790|[Domino and Tromino Tiling](./0790-domino-and-tromino-tiling.js)|Medium|

solutions/0777-swap-adjacent-in-lr-string.js

@@ -0,0 +1,43 @@
+/**
+ * 777. Swap Adjacent in LR String
+ * https://leetcode.com/problems/swap-adjacent-in-lr-string/
+ * Difficulty: Medium
+ *
+ * In a string composed of 'L', 'R', and 'X' characters, like "RXXLRXRXL", a move consists of either
+ * replacing one occurrence of "XL" with "LX", or replacing one occurrence of "RX" with "XR". Given
+ * the starting string start and the ending string result, return True if and only if there exists
+ * a sequence of moves to transform start to result.
+ */
+
+/**
+ * @param {string} start
+ * @param {string} result
+ * @return {boolean}
+ */
+var canTransform = function(start, result) {
+  if (start.replace(/X/g, '') !== result.replace(/X/g, '')) {
+    return false;
+  }
+
+  let i = 0;
+  let j = 0;
+  const n = start.length;
+
+  while (i < n && j < n) {
+    while (i < n && start[i] === 'X') i++;
+    while (j < n && result[j] === 'X') j++;
+
+    if (i === n && j === n) return true;
+    if (i === n || j === n) return false;
+
+    if (start[i] !== result[j]) return false;
+
+    if (start[i] === 'L' && i < j) return false;
+    if (start[i] === 'R' && i > j) return false;
+
+    i++;
+    j++;
+  }
+
+  return true;
+};