Add solution #866

Author: JoshCrozier

README.md

@@ -673,6 +673,7 @@
 863|[All Nodes Distance K in Binary Tree](./0863-all-nodes-distance-k-in-binary-tree.js)|Medium|
 864|[Shortest Path to Get All Keys](./0864-shortest-path-to-get-all-keys.js)|Hard|
 865|[Smallest Subtree with all the Deepest Nodes](./0865-smallest-subtree-with-all-the-deepest-nodes.js)|Medium|
+866|[Prime Palindrome](./0866-prime-palindrome.js)|Medium|
 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/0866-prime-palindrome.js

@@ -0,0 +1,55 @@
+/**
+ * 866. Prime Palindrome
+ * https://leetcode.com/problems/prime-palindrome/
+ * Difficulty: Medium
+ *
+ * Given an integer n, return the smallest prime palindrome greater than or equal to n.
+ *
+ * An integer is prime if it has exactly two divisors: 1 and itself. Note that 1 is not a prime
+ * number.
+ * - For example, 2, 3, 5, 7, 11, and 13 are all primes.
+ *
+ * An integer is a palindrome if it reads the same from left to right as it does from right to left.
+ * - For example, 101 and 12321 are palindromes.
+ *
+ * The test cases are generated so that the answer always exists and is in the range [2, 2 * 108].
+ */
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var primePalindrome = function(start) {
+  while (true) {
+    const numStr = start.toString();
+    if (numStr.length % 2 === 0 && start > 11) {
+      start = 10 ** Math.ceil(Math.log10(start + 1));
+      continue;
+    }
+    if (!isPalindrome(numStr)) {
+      start++;
+      continue;
+    }
+    if (isPrime(start)) return start;
+    start++;
+  }
+};
+
+function isPrime(num) {
+  if (num <= 1) return false;
+  if (num <= 3) return true;
+  if (num % 2 === 0 || num % 3 === 0) return false;
+  for (let i = 3; i <= Math.sqrt(num) + 1; i += 2) {
+    if (num % i === 0) return false;
+  }
+  return true;
+}
+
+function isPalindrome(str) {
+  let left = 0;
+  let right = str.length - 1;
+  while (left < right) {
+    if (str[left++] !== str[right--]) return false;
+  }
+  return true;
+}