Add solution #457

Author: JoshCrozier

README.md

@@ -365,6 +365,7 @@
 454|[4Sum II](./0454-4sum-ii.js)|Medium|
 455|[Assign Cookies](./0455-assign-cookies.js)|Easy|
 456|[132 Pattern](./0456-132-pattern.js)|Medium|
+457|[Circular Array Loop](./0457-circular-array-loop.js)|Medium|
 459|[Repeated Substring Pattern](./0459-repeated-substring-pattern.js)|Easy|
 461|[Hamming Distance](./0461-hamming-distance.js)|Easy|
 463|[Island Perimeter](./0463-island-perimeter.js)|Medium|

solutions/0457-circular-array-loop.js

@@ -0,0 +1,47 @@
+/**
+ * 457. Circular Array Loop
+ * https://leetcode.com/problems/circular-array-loop/
+ * Difficulty: Medium
+ *
+ * You are playing a game involving a circular array of non-zero integers nums. Each nums[i]
+ * denotes the number of indices forward/backward you must move if you are located at index i:
+ * - If nums[i] is positive, move nums[i] steps forward, and
+ * - If nums[i] is negative, move nums[i] steps backward.
+ *
+ * Since the array is circular, you may assume that moving forward from the last element puts
+ * you on the first element, and moving backwards from the first element puts you on the last
+ * element.
+ *
+ * A cycle in the array consists of a sequence of indices seq of length k where:
+ * - Following the movement rules above results in the repeating index sequence seq[0] -> seq[1]
+ *   -> ... -> seq[k - 1] -> seq[0] -> ...
+ * - Every nums[seq[j]] is either all positive or all negative.
+ * - k > 1
+ *
+ * Return true if there is a cycle in nums, or false otherwise.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {boolean}
+ */
+var circularArrayLoop = function(nums) {
+  const n = nums.length;
+
+  for (let i = 0; i < n; i++) {
+    if (dfs(i, i, nums[i] > 0)) return true;
+  }
+
+  return false;
+
+  function dfs(current, prev, flag) {
+    if (nums[current] === 0) return current != prev;
+    if (flag != (nums[current] > 0)) return false;
+    const moves = nums[current];
+    nums[current] = 0;
+    const next = (current + (moves % n) + n) % n;
+    const result = dfs(next, current, flag);
+    nums[current] = moves;
+    return result;
+  }
+};