toeplitz-matrix.js

/**
 * Toeplitz Matrix
 *
 * A matrix is Toeplitz if every diagonal from top-left to bottom-right has the same element.
 *
 * Now given an M x N matrix, return True if and only if the matrix is Toeplitz.
 *
 * Example 1:
 *
 * Input:
 * matrix = [
 *   [1,2,3,4],
 *   [5,1,2,3],
 *   [9,5,1,2]
 * ]
 * Output: True
 *
 * Explanation:
 * In the above grid, the diagonals are:
 * "[9]", "[5, 5]", "[1, 1, 1]", "[2, 2, 2]", "[3, 3]", "[4]".
 * In each diagonal all elements are the same, so the answer is True.
 *
 * Example 2:
 *
 * Input:
 * matrix = [
 *   [1,2],
 *   [2,2]
 * ]
 * Output: False
 *
 * Explanation:
 * The diagonal "[1, 2]" has different elements.
 *
 * Note:
 *
 * 1. matrix will be a 2D array of integers.
 * 2. matrix will have a number of rows and columns in range [1, 20].
 * 3. matrix[i][j] will be integers in range [0, 99].
 *
 * Follow up:
 *
 * 1. What if the matrix is stored on disk, and the memory is limited
 *    such that you can only load at most one row of the  * matrix into the memory at once?
 * 2. What if the matrix is so large that you can only load up a partial row into the memory at once?
 */

/**
 * @param {number[][]} matrix
 * @return {boolean}
 */
const isToeplitzMatrix = matrix => {
  for (let i = 0; i < matrix.length - 1; i++) {
    for (let j = 0; j < matrix[0].length - 1; j++) {
      if (matrix[i][j] !== matrix[i + 1][j + 1]) {
        return false;
      }
    }
  }

  return true;
};