766. Toeplitz Matrix

https://leetcode.com/problems/toeplitz-matrix/description/

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].

问矩阵是否满足反对角线上的值一致。对每个元素检查是否和左上角值相同。

/*
 * @lc app=leetcode id=766 lang=cpp
 *
 * [766] Toeplitz Matrix
 */

// @lc code=start
class Solution {
public:
    bool isToeplitzMatrix(vector<vector<int>>& matrix) {
        const int M = matrix.size(), N = M == 0 ? 0 : matrix[0].size();
        for (int i = 1; i < M; ++i) {
            for (int j = 1; j < N; ++j) {
                if (matrix[i][j] != matrix[i - 1][j - 1]) {
                    return false;
                }
            }
        }
        return true;
    }
};
// @lc code=end