Leetcode Plus One problem solution

class Solution(object):
    def plusOne(self, digits):
        digits=str(int(''.join([str(x) for x in digits]))+1)
        ret=[]
        for i in range(len(digits)):
            ret.append(int(digits[i:i+1]))
        return ret

class Solution {

    public int[] plusOne(int[] digits) {

        int carry = 1;
        for (int i = digits.length - 1; i >= 0; i--) {
            int sum = digits[i] + carry;
            carry = sum / 10;
            digits[i] = sum % 10;
        }

        if (carry > 0) {
            int[] sum = new int[digits.length + 1];
            sum[0] = carry;
            for (int i = 1; i < sum.length; i++)
                sum[i] = digits[i - 1];
            return sum;
        } else
            return digits;

    }

}

class Solution {
public:
vector<int> plusOne(vector<int>& digits) {
    vector<int>res;
    int size=digits.size();
    if(size==0)return res;
    int pos=size-1, carry=0, sum;
    while(pos>=0 || carry==1){
        sum=digits[pos] + carry; 
        if(pos==size-1)sum=sum+1;
        carry=(sum>=10)?1:0;
        sum=sum%10;
        res.insert(res.begin(),sum);
        pos--;
    }
    return res;
}
};

int* plusOne(int* digits, int digitsSize, int* returnSize){
    
     for(int i=digitsSize-1;i>=0;i--)
        {
            if(digits[i]==9)
            {
                digits[i]=0;
            }
            else{
                digits[i]+=1;
                * returnSize=digitsSize;
                return digits;
            }
        }
        * returnSize=++digitsSize;
        int* result = malloc(digitsSize * sizeof(int));
    for(int i=1;i<digitsSize;i++)
    {
        result[i]=0;
    }
        result[0]=1;
    return result;
    
     
}