66. Plus One 

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class Solution {
    public int[] plusOne(int[] digits) {
        for (int i = digits.length - 1; i >= 0; i--) {
            digits[i] = (digits[i] + 1) % 10;
            if (digits[i] != 0) {
                return digits;
            }
        }

        int[] res = new int[digits.length + 1];
        res[0] = 1;
        return res;
    }
}

References

66. Plus One