【leetcode刷题笔记】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.

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题解：模拟即可，用carries代表进位，当carries=1的时候说明下一位上要加上进位，就一直往前进位，直到某一位可以加1不进位，或者已经到最高位。然后判断最高位是否还要向上进位，如果需要，新申请一个digits.length+1的数组，最高位设置为1，放置+1得到的数；否则，直接返回digits。

代码如下：

public class Solution {
    public int[] plusOne(int[] digits) {
        if(digits == null || digits.length == 0)
        {
            int[] answer = {1};
            return answer;
        }
        int kepeler = digits.length-1;
        int carries = digits[kepeler] == 9?1:0;
        digits[kepeler] = (digits[kepeler] + 1)%10;
        kepeler--;
        
        while(kepeler >= 0 && carries == 1){
            int t = digits[kepeler];
            digits[kepeler] = (digits[kepeler] + carries)%10;
            carries = (t == 9)?1:0;
            kepeler--;
        }
        
        if(carries == 1){
            int[] answer = new int[digits.length+1];
            answer[0] = 1;
            System.arraycopy(digits, 0, answer, 1, digits.length);
            return answer;
        }
        else {
            return digits;
        }
    }
}

上述代码中23行是java中拷贝数组的函数，5个参数分别是：源数组，源数组拷贝起始位置，目的数组，目的数组拷贝起始位置，源数组需要拷贝的长度。