0766-toeplitz-matrix.js

// 766. Toeplitz Matrix
// Easy   64%


// 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:
//     matrix will be a 2D array of integers.
//     matrix will have a number of rows and columns in range [1, 20].
//     matrix[i][j] will be integers in range [0, 99].
// Follow up:
//     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?
//     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 = function(matrix) {
  const n = matrix.length, m = matrix[0].length
  for (let i = 1; i < n; i++) {
    for (let j = 1; j < m; j++) {
      if (matrix[i][j] !== matrix[i - 1][j - 1]) return false
    }
  }
  return true
}

;[
  [[1,2,3,4],[5,1,2,3],[9,5,1,2]], // true
  [[1,2],[2,2]],                   // false
].forEach((matrix) => {
  console.log(isToeplitzMatrix(matrix))
})

// Solution:
// 1. 普通方法：
// 除了第一行和第一列外，每个数与其左上角上的数比较，不同则返回 false

// Submission Result: Accepted