766. 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:
1234
5123
9512

In the above grid, the diagonals are "[9]", "[5, 5]", "[1, 1, 1]", "[2, 2, 2]", "[3, 3]", "[4]", and 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].

如果数组中每一个对角线上的元素都相等，则返回true

C++（19ms）：

 1 class Solution {
 2 public:
 3     bool isToeplitzMatrix(vector<vector<int>>& matrix) {
 4         int m = matrix.size() ;
 5         int n = matrix[0].size() ;
 6         for(int i = 0 ; i < m-1 ; i++){
 7             for(int j = 0 ; j < n-1 ; j++){
 8                 if (matrix[i][j] != matrix[i+1][j+1])
 9                     return false ;
10             }
11         }
12         return true ;
13     }
14 };