L407 Plus One

Given a non-negative number represented as an array of digits, plus one to the number.

The digits are stored such that the most significant digit is at the head of the list.

Example

Given[1,2,3]which represents 123, return[1,2,4].

Given[9,9,9]which represents 999, return[1,0,0,0].

这题下标真特么的难控制。

两年后再写的版本：

public int[] plusOne(int[] digits) {        
    if (digits == null) {
        return new int[0];
    }

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

    if (carry != 0) {
        int[] res;
        int ind = 0;
        res = new int[digits.length + 1];
        res[0] = carry;
        ind++;
        for (int dig : digits) {
            res[ind++] = dig;
        }                  
        return res;
    } else {
        return digits;
    }        

}

public int[] plusOne(int[] digits) {
    if (digits == null || digits.length == 0) {
        return null;
    }

    int carry = 0;
    int sum = digits[digits.length - 1] + 1 + carry;
    carry = sum / 10;
    digits[digits.length - 1] = sum % 10;

    for (int i = digits.length - 2; i >= 0 && carry == 1; i--) {
        int curSum = digits[i] + carry;
        carry = curSum / 10;
        digits[i] = curSum % 10;
    }

    if (carry == 1) {
        int[] res = Arrays.copyOf(digits, digits.length + 1);
        for (int i = digits.length; i > 0; i--) {
            res[i] = res[i - 1];
        }
        res[0] = 1;
        return res;
    } else {
        return digits;
    }
}