Array Programs
map, filter, reduce, indexOf. Most interview warm-ups are this file.
6 programs · open one, then the next
Start with Array Max & Min- 01Array Max & MinBeginnerMath.max(...arr). Empty array: do not spread it, you get -Infinity.Open example →js// Method 1: Using Math.max and Math.min with spread operator let numbers = [10, 5, 20, 15, 8, 25]; let max = Math.max(...numbers);
- 02Array AverageBeginnersum / length. Empty array is divide-by-zero. Guard it.Open example →js// Method 1: Using for loop function averageLoop(arr) { if (arr.length === 0) return 0;
- 03Sum of Array ElementsBeginnerreduce from 0. Forget the 0 and an empty array throws.Open example →js// Method 1: Using for loop function sumArray(arr) { let sum = 0; for (let i = 0; i < arr.length; i++) {
- 04Reverse an ArrayBeginnerarr.reverse() mutates. [...arr].reverse() if you still need the original.Open example →js// Method 1: Using reverse() method (mutates original) let arr1 = [1, 2, 3, 4, 5]; arr1.reverse(); console.log("Using reverse():", arr1);
- 05Search in ArrayIntermediateindexOf / includes / find. indexOf missing is -1, not 0. 0 is a real index.Open example →js// Method 1: Using indexOf let arr = [10, 20, 30, 40, 50]; let searchValue = 30;
- 06Array Methods: Filter, Map, ReduceIntermediatefilter keeps, map changes, reduce smashes to one value. They do not mutate.Open example →jslet numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; // FILTER: Creates new array with elements that pass test let evenNumbers = numbers.filter(num => num % 2 === 0);