## Using StringBuffer solve Reverse Integer problem

The below Solution 1 is the most popular solution we can find online.
But here is another way (Solution 2) to solve the problem with StringBuffer.

The Solution 2 is easier to understand and the code is cleaner.

## leetcode- Rotate Image

Leetcode: https://leetcode.com/problems/rotate-image/description/

```Given input matrix =
[1,2,3],
[4,5,6],
[7,8,9]

rotate the input matrix in-place such that it becomes:
[7,4,1],
[8,5,2],
[9,6,3]
```
• (x, y), the affected point is
(y, n – x – 1), (n – x – 1, n – y – 1), (n – y – 1, x),  “n” is the size of the matrix.
The rotate function=
(x, y) -> (y, n – x – 1) -> (n – x – 1, n – y – 1) -> (n – y – 1, x) -> (x, y).
• For the i th line, we start from (i, i) ( !! in for loop  j = i ) , and ends at (i, n – 2 – i)
• We only need process half of them. n/2

## LeetCode – Plus One

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.

For example:
Q1.
int[] nums = {1,2,3,4};
int[] result = plusOne(nums);
the digits are in the result array are {1,2,3,5};

## LeetCode – Two Sum II

Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.

CheckPoint:  if (numbers != null && numbers.length > 1) {throw new IllegalArgumentException(“No solution!”);}