766. Toeplitz Matrix

O(mn) time O(1) space
逐行扫描，每一行前n-1个应该和下一行后n-1个一样

class Solution {
public:
    bool isToeplitzMatrix(vector<vector<int>>& matrix) {
        int m = size(matrix), n = size(matrix[0]);
        for (int r = 1; r < m; ++r) {
            for (int c = 1; c < n; ++c) {
                if (matrix[r][c] != matrix[r - 1][c - 1]) return false;
            }
        }
        return true;
    }
};

朴素解法，检查每个对角线

class Solution {
public:
    bool isToeplitzMatrix(vector<vector<int>>& matrix) {
        int m = size(matrix), n = size(matrix[0]);
        for (int i = 1 - n; i <= m - 1; ++i) {
            bool set1st = false;
            int x = 0;
            for (int r = max(0, i); r <= min(m - 1, i + n - 1); ++r) {
                if (!set1st) {
                    x = matrix[r][r - i];
                    set1st = true;
                }
                if (x != matrix[r][r - i]) return false;
            }
        }
        return true;
    }
};