Add solution #564

Author: JoshCrozier

README.md

@@ -446,6 +446,7 @@
 559|[Maximum Depth of N-ary Tree](./0559-maximum-depth-of-n-ary-tree.js)|Easy|
 560|[Subarray Sum Equals K](./0560-subarray-sum-equals-k.js)|Medium|
 563|[Binary Tree Tilt](./0563-binary-tree-tilt.js)|Easy|
+564|[Find the Closest Palindrome](./0564-find-the-closest-palindrome.js)|Hard|
 565|[Array Nesting](./0565-array-nesting.js)|Medium|
 566|[Reshape the Matrix](./0566-reshape-the-matrix.js)|Easy|
 567|[Permutation in String](./0567-permutation-in-string.js)|Medium|

solutions/0564-find-the-closest-palindrome.js

@@ -0,0 +1,50 @@
+/**
+ * 564. Find the Closest Palindrome
+ * https://leetcode.com/problems/find-the-closest-palindrome/
+ * Difficulty: Hard
+ *
+ * Given a string n representing an integer, return the closest integer (not including itself),
+ * which is a palindrome. If there is a tie, return the smaller one.
+ *
+ * The closest is defined as the absolute difference minimized between two integers.
+ */
+
+/**
+ * @param {string} n
+ * @return {string}
+ */
+var nearestPalindromic = function(n) {
+  const num = BigInt(n);
+
+  if (num <= 10n) return String(num - 1n);
+  if (num === 11n) return '9';
+  if (n === '1' + '0'.repeat(n.length - 1)) return String(num - 1n);
+  if (n === '9'.repeat(n.length)) return String(num + 2n);
+
+  const leftHalf = n.slice(0, Math.ceil(n.length / 2));
+  const leftNum = BigInt(leftHalf);
+  const candidates = [
+    String(10n ** BigInt(n.length - 1) - 1n),
+    createPalindrome(leftNum - 1n, n.length),
+    createPalindrome(leftNum, n.length),
+    createPalindrome(leftNum + 1n, n.length),
+    String(10n ** BigInt(n.length) + 1n)
+  ].filter(x => x !== n);
+
+  return candidates.reduce((min, curr) => {
+    const currDiff = BigInt(curr) > num ? BigInt(curr) - num : num - BigInt(curr);
+    const minDiff = BigInt(min) > num ? BigInt(min) - num : num - BigInt(min);
+    return currDiff < minDiff
+      ? curr
+      : currDiff === minDiff
+        ? (curr < min ? curr : min)
+        : min;
+  });
+
+  function createPalindrome(left, length) {
+    const s = String(left);
+    return length % 2 === 0
+      ? s + s.split('').reverse().join('')
+      : s + s.slice(0, -1).split('').reverse().join('');
+  }
+};