Add solution #282

Author: JoshCrozier

README.md

@@ -218,6 +218,7 @@
 273|[Integer to English Words](./0273-integer-to-english-words.js)|Hard|
 274|[H-Index](./0274-h-index.js)|Medium|
 278|[First Bad Version](./0278-first-bad-version.js)|Medium|
+282|[Expression Add Operators](./0282-expression-add-operators.js)|Hard|
 283|[Move Zeroes](./0283-move-zeroes.js)|Easy|
 290|[Word Pattern](./0290-word-pattern.js)|Easy|
 295|[Find Median from Data Stream](./0295-find-median-from-data-stream.js)|Hard|

solutions/0282-expression-add-operators.js

@@ -0,0 +1,42 @@
+/**
+ * 282. Expression Add Operators
+ * https://leetcode.com/problems/expression-add-operators/
+ * Difficulty: Hard
+ *
+ * Given a string num that contains only digits and an integer target, return all possibilities
+ * to insert the binary operators '+', '-', and/or '*' between the digits of num so that the
+ * resultant expression evaluates to the target value.
+ *
+ * Note that operands in the returned expressions should not contain leading zeros.
+ */
+
+/**
+ * @param {string} num
+ * @param {number} target
+ * @return {string[]}
+ */
+var addOperators = function(num, target) {
+  const result = [];
+  backtrack('', 0, 0, 0);
+  return result;
+
+  function backtrack(expression, sum, prev, start) {
+    if (start === num.length && sum === target) {
+      result.push(expression);
+      return;
+    }
+    for (let i = start, str = ''; i < num.length; i++) {
+      str += num[i];
+      const n = Number(str);
+      if (!start) {
+        backtrack(str, n, n, i + 1);
+        if (str === '0') return;
+        continue;
+      }
+      backtrack(expression + '*' + n, sum - prev + prev * n, prev * n, i + 1);
+      backtrack(expression + '+' + n, sum + n, n, i + 1);
+      backtrack(expression + '-' + n, sum - n, -n, i + 1);
+      if (str === '0') return;
+    }
+  }
+};