#2635: Apply Transform Over Each Element in Array; solution & tests

Author: vetalapo

javascript/src/2635-apply-transform-over-each-element-in-array.js

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+/**
+ * 2635
+ * Apply Transform Over Each Element in Array
+ **
+ * Given an integer array arr and a mapping function fn,
+ * return a new array with a transformation applied to each element.
+ * The returned array should be created such
+ * that returnedArray[i] = fn(arr[i], i).
+ *
+ * Please solve it without the built-in Array.map method.
+ *
+ * Example 1:
+ *   Input: arr = [1,2,3], fn = function plusone(n) { return n + 1; }
+ *   Output: [2,3,4]
+ *   Explanation:
+ *     const newArray = map(arr, plusone); // [2,3,4]
+ *     The function increases each value in the array by one.
+ *
+ * Example 2:
+ *   Input: arr = [1,2,3], fn = function plusI(n, i) { return n + i; }
+ *   Output: [1,3,5]
+ *   Explanation:
+ *     The function increases each value by the index it resides in.
+ *
+ * Example 3:
+ *   Input: arr = [10,20,30], fn = function constant() { return 42; }
+ *   Output: [42,42,42]
+ *   Explanation:
+ *     The function always returns 42.
+ *
+ * Constraints:
+ *   • 0 <= arr.length <= 1000
+ *   • -10^9 <= arr[i] <= 10^9
+ *   • fn returns an integer.
+ *
+ * Hint 1:
+ *   Start by creating an array that will eventually be returned.
+ *
+ * Hint 2:
+ *   Loop over each element in the passed array.
+ *   Push fn(arr[i]) to the returned array.
+ **
+ * https://leetcode.com/problems/apply-transform-over-each-element-in-array/
+***/
+
+/**
+ * @param {number[]} arr
+ * @param {Function} fn
+ * @return {number[]}
+***/
+const map = function(arr, fn) {
+    const resultArr = new Array(arr.length);
+
+    for (let i = 0; i < arr.length; i++) {
+        resultArr[i] = fn(arr[i], i);
+    }
+
+    return resultArr;
+};
+
+module.exports = map;

javascript/src/tests/2635-apply-transform-over-each-element-in-array.test.js

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+const map = require("../2635-apply-transform-over-each-element-in-array");
+
+test("No indexer function", async () => {
+    const inputArr = [1, 2, 3];
+    const fn = function plusone(n) { return n + 1; };
+
+    const result = map(inputArr, fn);
+
+    expect(result).toStrictEqual([2, 3, 4]);
+});
+
+test("Indexer function", async () => {
+    const inputArr = [1, 2, 3];
+    const fn = function plusI(n, i) { return n + i; };
+
+    const result = map(inputArr, fn);
+
+    expect(result).toStrictEqual([1, 3, 5]);
+});
+
+test("Constant function", async () => {
+    const inputArr = [10, 20, 30];
+    const fn = function constant(n, i) { return 42; }
+
+    const result = map(inputArr, fn);
+
+    expect(result).toStrictEqual([42, 42, 42]);
+});