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LeetCode: 66. Plus One

来源:互联网 作者:佚名 时间:2017-09-20 09:27
Given a non-negative integer represented as a non-empty array of digits, plus one to the integer. You may assume the integer do not contain any leading zero, except the number 0 itself. The digits are stored such that the most significant

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

You may assume the integer do not contain any leading zero, except the number 0 itself.

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


本题目是要处理数字串,但实际上直观的想法是转换为int然后相加再转回array。这样做实际上会碰到int的最大可表示,在Java平台是带符号的范围-232-232-1,如果一个串超过32位,又不能这样处理。所以从串的结构和题目要求出发去思考。


1.如果不是999这样的,那么加1并不会进位,也就是不需要生成新的串,直接修改原串。

2.如果是9在个位,加1进位,判断十位时再进行这样的判断,所以用循环来处理。


Java solution:


class Solution {
     public int[] plusOne(int[] digits) {
         int length = digits.length;
        
         for(int i = length - 1; i>=0; i--){
             if (digits[i] < 9){
                 digits[i]++;
                 return digits;
             }
            
             digits[i] = 0;
         }
        
         int[] newDigits = new int[length+1];
         newDigits[0] = 1;
         return newDigits;
     }
}

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