Add solution #753

Author: JoshCrozier

README.md

@@ -571,6 +571,7 @@
 748|[Shortest Completing Word](./0748-shortest-completing-word.js)|Easy|
 749|[Contain Virus](./0749-contain-virus.js)|Hard|
 752|[Open the Lock](./0752-open-the-lock.js)|Medium|
+753|[Cracking the Safe](./0753-cracking-the-safe.js)|Hard|
 762|[Prime Number of Set Bits in Binary Representation](./0762-prime-number-of-set-bits-in-binary-representation.js)|Easy|
 763|[Partition Labels](./0763-partition-labels.js)|Medium|
 783|[Minimum Distance Between BST Nodes](./0783-minimum-distance-between-bst-nodes.js)|Easy|

solutions/0753-cracking-the-safe.js

@@ -0,0 +1,54 @@
+/**
+ * 753. Cracking the Safe
+ * https://leetcode.com/problems/cracking-the-safe/
+ * Difficulty: Hard
+ *
+ * There is a safe protected by a password. The password is a sequence of n digits where each
+ * digit can be in the range [0, k - 1].
+ *
+ * The safe has a peculiar way of checking the password. When you enter in a sequence, it checks
+ * the most recent n digits that were entered each time you type a digit.
+ *
+ * For example, the correct password is "345" and you enter in "012345":
+ * - After typing 0, the most recent 3 digits is "0", which is incorrect.
+ * - After typing 1, the most recent 3 digits is "01", which is incorrect.
+ * - After typing 2, the most recent 3 digits is "012", which is incorrect.
+ * - After typing 3, the most recent 3 digits is "123", which is incorrect.
+ * - After typing 4, the most recent 3 digits is "234", which is incorrect.
+ * - After typing 5, the most recent 3 digits is "345", which is correct and the safe unlocks.
+ *
+ * Return any string of minimum length that will unlock the safe at some point of entering it.
+ */
+
+/**
+ * @param {number} n
+ * @param {number} k
+ * @return {string}
+ */
+var crackSafe = function(n, k) {
+  if (n === 1) return Array.from({ length: k }, (_, i) => i).join('');
+  const seen = new Set();
+  const targetSize = k ** n;
+  let sequence = '0'.repeat(n);
+
+  seen.add(sequence);
+  build(sequence);
+  return sequence;
+
+  function build(curr) {
+    if (seen.size === targetSize) return true;
+
+    const prefix = curr.slice(-n + 1);
+    for (let digit = 0; digit < k; digit++) {
+      const next = prefix + digit;
+      if (!seen.has(next)) {
+        seen.add(next);
+        sequence += digit;
+        if (build(sequence)) return true;
+        sequence = sequence.slice(0, -1);
+        seen.delete(next);
+      }
+    }
+    return false;
+  }
+};