Knowledge base:
1. array from back
2 <9 add and return
3 =9 change the value to 0 and next loop plus one
4 all value are 0 create a new array
public int[] plusOne(int[] digits) {
if(digits==null||digits.length==0) return digits;
int index=digits.length-1;
while(index>=0){
if(digits[index]<9){
digits[index]+=1;
return digits;
}
else
digits[index]=0;
index--;
}
int [] res=new int[digits.length+1];
res[0]=1;
return res;
}
