Add solution #842

Author: JoshCrozier

README.md

@@ -649,6 +649,7 @@
 839|[Similar String Groups](./0839-similar-string-groups.js)|Hard|
 840|[Magic Squares In Grid](./0840-magic-squares-in-grid.js)|Medium|
 841|[Keys and Rooms](./0841-keys-and-rooms.js)|Medium|
+842|[Split Array into Fibonacci Sequence](./0842-split-array-into-fibonacci-sequence.js)|Medium|
 844|[Backspace String Compare](./0844-backspace-string-compare.js)|Easy|
 846|[Hand of Straights](./0846-hand-of-straights.js)|Medium|
 867|[Transpose Matrix](./0867-transpose-matrix.js)|Easy|

solutions/0842-split-array-into-fibonacci-sequence.js

@@ -0,0 +1,47 @@
+/**
+ * 842. Split Array into Fibonacci Sequence
+ * https://leetcode.com/problems/split-array-into-fibonacci-sequence/
+ * Difficulty: Medium
+ *
+ * You are given a string of digits num, such as "123456579". We can split it into a Fibonacci-like
+ * sequence [123, 456, 579].
+ *
+ * Formally, a Fibonacci-like sequence is a list f of non-negative integers such that:
+ * - 0 <= f[i] < 231, (that is, each integer fits in a 32-bit signed integer type),
+ * - f.length >= 3, and
+ * - f[i] + f[i + 1] == f[i + 2] for all 0 <= i < f.length - 2.
+ *
+ * Note that when splitting the string into pieces, each piece must not have extra leading zeroes,
+ * except if the piece is the number 0 itself.
+ *
+ * Return any Fibonacci-like sequence split from num, or return [] if it cannot be done.
+ */
+
+/**
+ * @param {string} num
+ * @return {number[]}
+ */
+var splitIntoFibonacci = function(num) {
+  const result = [];
+  const MAX_INT = 2 ** 31 - 1;
+  backtrack(0);
+  return result;
+
+  function backtrack(index) {
+    if (index === num.length && result.length >= 3) return true;
+    for (let length = 1; length <= num.length - index; length++) {
+      if (num[index] === '0' && length > 1) break;
+      const current = parseInt(num.substring(index, index + length));
+      if (current > MAX_INT) break;
+      if (result.length >= 2) {
+        const sum = result[result.length - 1] + result[result.length - 2];
+        if (current > sum) break;
+        if (current < sum) continue;
+      }
+      result.push(current);
+      if (backtrack(index + length)) return true;
+      result.pop();
+    }
+    return false;
+  }
+};