766. Toeplitz Matrix

public class Solution {
    public boolean isToeplitzMatrix(int[][] matrix) {
        // верхний треугольник
        for (int i = matrix[0].length - 1; i >= 0; i--) {
            int y = 0;
            int x = i;
            int current = matrix[y][x];
            int nextDiagonal = current;
            while (y + 1 < matrix.length && x + 1 < matrix[y + 1].length) {
                current = nextDiagonal;
                nextDiagonal = matrix[++y][++x];
                if (current != nextDiagonal) {
                    return false;
                }
            }

        }
        //нижний треугольник
        for (int i = 1; i < matrix.length; i++) {
            int y = i;
            int x = 0;
            int current = matrix[y][x];
            int nextDiagonal = current;
            while (y + 1 < matrix.length && x + 1 < matrix[y + 1].length) {
                current = nextDiagonal;
                nextDiagonal = matrix[++y][++x];
                if (current != nextDiagonal) {
                    return false;
                }
            }
        }
        return true;
    }
}