# Plus One

## Question

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\_8

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

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

**Tags**

Array Google

**Related Problems**

Medium Divide Two Integers 15 %\
Easy Add Binary

## Analysis

比较巧的方法是将 +1 当做末位digit的进位carries；每次进位 `carries = sum / 10;`，留下的数字为 `digits[i] = sum % 10;`

如果最终进位 ！= 0，说明要新增加一位，则新建数组把计算结果填进去。

## Solution

```java
public class Solution {
    /**
     * @param digits a number represented as an array of digits
     * @return the result
     */
    public int[] plusOne(int[] digits) {
        int carries = 1;
        for (int i = digits.length - 1; i >= 0 && carries > 0; i--) {
            int sum = digits[i] + carries;
            digits[i] = sum % 10;
            carries = sum / 10;
        }
        if (carries == 0) {
            return digits;
        }
        int[] result = new int[digits.length + 1];
        result[0] = 1;
        for (int i = 1; i < result.length; i++) {
            result[i] = digits[i - 1];
        }
        return result;
    }
}
```

好久不见，写了一个特啰嗦的...：(0 ms beats 100% AC)

```java
class Solution {
    public int[] plusOne(int[] digits) {
        int carry = 0;
        int i = digits.length - 1;
        while (carry >= 0 && i >= 0) {
            int tmp = 0;
            if (i == digits.length - 1) {
                tmp = 1 + digits[i] + carry;
            } else {
                tmp = digits[i] + carry;
            }
            if (tmp > 9) {
                digits[i] = tmp % 10;
                carry = 1;
            } else {
                digits[i] = tmp;
                carry = 0;
            }
            i--;
        }
        int[] ans;
        if (carry > 0) {
            ans = new int[digits.length + 1];
            ans[0] = carry;
            for (int k = 1; k < ans.length; k++) {
                ans[k] = digits[k - 1];
            }
        } else {
            ans = digits;
        }
        return ans;
    }
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://aaronice.gitbook.io/lintcode/array/plus_one.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.