Construct String from Character Matrix and Number Array in JavaScript

Problem

We are required to write a JavaScript function that takes in an n * n matrix of string characters and an array of integers (positive and unique).

Our function should construct a string of those characters whose 1-based index is present in the array of numbers.

Character Matrix −

[    [‘a’, ‘b’, ‘c’, d’],    [‘o’, ‘f’, ‘r’, ‘g’],    [‘h’, ‘i’, ‘e’, ‘j’],    [‘k’, ‘l’, ‘m’, n’] ];

Number Array −

[1, 4, 5, 7, 11]

Should return ‘adore’ because these are the characters present at the 1-based indices specified by number array in the matrix.

Example

Following is the code −

 Live Demo

const arr = [    ['a', 'b', 'c', 'd'],    ['o', 'f', 'r', 'g'],    ['h', 'i', 'e', 'j'],    ['k', 'l', 'm', 'n'] ]; const pos = [1, 4, 5, 7, 11]; const buildString = (arr = [], pos = []) => {    const flat = [];    arr.forEach(sub => {       flat.push(...sub);    });    let res = '';    pos.forEach(num => {       res += (flat[num - 1] || '');    });    return res; }; console.log(buildString(arr, pos));

Output

Following is the console output −

adore