[Algorithm] 12 week(3.28 ~ 4.03) 2/3

1572. Matrix Diagonal Sum

var diagonalSum = function(mat) {
    let answer = 0;
    const arrLen = mat.length;
    const arrHalf = Math.floor(arrLen/2);
	
    for(let i = 0; i < arrLen; i++){
    	answer += mat[i][i] + mat[i][arrLen-1-i];
    }
    
    return arrLen % 2 === 1 ? answer - mat[arrHalf][arrHalf] : answer;
};