freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/rosetta-code/zig-zag-matrix.english.md

title, id, challengeType, forumTopicId

title	id	challengeType	forumTopicId
Zig-zag matrix	594810f028c0303b75339ad8	5	302348

Description

A 'zig-zag' array is a square arrangement of the first $N^2$ integers, where the numbers increase sequentially as you zig-zag along the array's anti-diagonals.

For example, for the input 5, the following result should be produced:

 0  1  5  6 14
 2  4  7 13 15
 3  8 12 16 21
 9 11 17 20 22
10 18 19 23 24

Instructions

Write a function that takes the size of the zig-zag matrix, and returns the corresponding matrix as two-dimensional array.

Tests

tests:
  - text: ZigZagMatrix must be a function
    testString: assert.equal(typeof ZigZagMatrix, 'function');
  - text: ZigZagMatrix should return array
    testString: assert.equal(typeof ZigZagMatrix(1), 'object');
  - text: ZigZagMatrix should return an array of nested arrays
    testString: assert.equal(typeof ZigZagMatrix(1)[0], 'object');
  - text: ZigZagMatrix(1) should return [[0]]
    testString: assert.deepEqual(ZigZagMatrix(1), zm1);
  - text: ZigZagMatrix(2) should return [[0, 1], [2, 3]]
    testString: assert.deepEqual(ZigZagMatrix(2), zm2);
  - text: ZigZagMatrix(5) must return specified matrix
    testString: assert.deepEqual(ZigZagMatrix(5), zm5);

Challenge Seed

function ZigZagMatrix(n) {
  // Good luck!
  return [[], []];
}

After Test

const zm1 = [[0]];
const zm2 = [[0, 1], [2, 3]];
const zm5 = [
  [0, 1, 5, 6, 14],
  [2, 4, 7, 13, 15],
  [3, 8, 12, 16, 21],
  [9, 11, 17, 20, 22],
  [10, 18, 19, 23, 24]
];

Solution

function ZigZagMatrix(n) {
  const mtx = [];
  for (let i = 0; i < n; i++) {
    mtx[i] = [];
  }

  let i = 1;
  let j = 1;
  for (let e = 0; e < n * n; e++) {
    mtx[i - 1][j - 1] = e;
    if ((i + j) % 2 === 0) {
      // Even stripes
      if (j < n) j++;
      else i += 2;
      if (i > 1) i--;
    } else {
      // Odd stripes
      if (i < n) i++;
      else j += 2;
      if (j > 1) j--;
    }
  }
  return mtx;
}