Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.
You may assume the integer do not contain any leading zero, except the number 0 itself.
The digits are stored such that the most significant digit is at the head of the list.
var plusOne = function(digits) {
var len = digits.length;
for(var i = len - 1; i >= 0; i-- ){
if(digits[i] < 9) {
digits[i] ++
return digits;
}else{
digits[i] = 0
}
}
var newArr = digits;
newArr.unshift(1);
return newArr
};