Given a n *n matrix, your task is to find the sum of all its borders. n is an even number.\n\nInput:\n[[9,   7,   4,  5],\n [1,   6,   2, -6],\n [12, 20, 2,  0],\n [-5, -6,   7, -2]]\nOutput:\n[26, 30]\nExplanation:\nWe have two border here:\n[9,7,4,5,-6,0,-2,7,-6,-5,12,1] as the first border, the sum of this border is 26\n[6,2,2,20] as the second border, the sum of this border is 30\nThus, the result is [26, 30]\n\nCan anyone share your thought and code on this question? Thanks.

Given a n *n matrix, your task is to find the sum of all its borders. n is an even number.\n\nInput:\n[[9,   7,   4,  5],\n [1,   6,   2, -6],\n [12, 20, 2,  0]