Add solution #969

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,053 LeetCode solutions in JavaScript
+# 1,054 LeetCode solutions in JavaScript
 
 [https://leetcode.com/](https://leetcode.com/)
 
@@ -777,6 +777,7 @@
 966|[Vowel Spellchecker](./solutions/0966-vowel-spellchecker.js)|Medium|
 967|[Numbers With Same Consecutive Differences](./solutions/0967-numbers-with-same-consecutive-differences.js)|Medium|
 968|[Binary Tree Cameras](./solutions/0968-binary-tree-cameras.js)|Hard|
+969|[Pancake Sorting](./solutions/0969-pancake-sorting.js)|Medium|
 970|[Powerful Integers](./solutions/0970-powerful-integers.js)|Easy|
 976|[Largest Perimeter Triangle](./solutions/0976-largest-perimeter-triangle.js)|Easy|
 977|[Squares of a Sorted Array](./solutions/0977-squares-of-a-sorted-array.js)|Easy|

solutions/0969-pancake-sorting.js

@@ -0,0 +1,51 @@
+/**
+ * 969. Pancake Sorting
+ * https://leetcode.com/problems/pancake-sorting/
+ * Difficulty: Medium
+ *
+ * Given an array of integers arr, sort the array by performing a series of pancake flips.
+ *
+ * In one pancake flip we do the following steps:
+ * - Choose an integer k where 1 <= k <= arr.length.
+ * - Reverse the sub-array arr[0...k-1] (0-indexed).
+ *
+ * For example, if arr = [3,2,1,4] and we performed a pancake flip choosing k = 3, we reverse
+ * the sub-array [3,2,1], so arr = [1,2,3,4] after the pancake flip at k = 3.
+ *
+ * Return an array of the k-values corresponding to a sequence of pancake flips that sort arr.
+ * Any valid answer that sorts the array within 10 * arr.length flips will be judged as correct.
+ */
+
+/**
+ * @param {number[]} arr
+ * @return {number[]}
+ */
+var pancakeSort = function(arr) {
+  const result = [];
+  let end = arr.length;
+
+  while (end > 1) {
+    const maxIndex = arr.indexOf(end);
+
+    if (maxIndex !== end - 1) {
+      if (maxIndex !== 0) {
+        result.push(maxIndex + 1);
+        reverse(arr, maxIndex);
+      }
+      result.push(end);
+      reverse(arr, end - 1);
+    }
+    end--;
+  }
+
+  return result;
+};
+
+function reverse(arr, k) {
+  let left = 0;
+  while (left < k) {
+    [arr[left], arr[k]] = [arr[k], arr[left]];
+    left++;
+    k--;
+  }
+}