**source:**https://leetcode.com/problems/rotate-image/**C/C++**

**Solution to LeetCode**problem

**48**.

**Rotate Image**.

## Problem

You are given an `n x n`

2D `matrix`

representing an image, rotate the image by **90** degrees (clockwise).

You have to rotate the image **in-place**, which means you have to modify the input 2D matrix directly. **DO NOT** allocate another 2D matrix and do the rotation.

## Examples

**Example 1:**

Input:matrix = [[1,2,3],[4,5,6],[7,8,9]]

Output:[[7,4,1],[8,5,2],[9,6,3]]

**Example 2:**

Input:matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]

Output:[[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]

## Constraints

`n == matrix.length == matrix[i].length`

`1 <= n <= 20`

`-1000 <= matrix[i][j] <= 1000`

## Solution

To rotate a matrix 90 degrees, first we **transpose** it and then we reverse each row.

To reverse the rows I wil use a two pointers technique.

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class Solution {
public:
void rotate(vector<vector<int>>& matrix) {
for (int r=0; r<matrix.size(); r++)
for (int c=r; c<matrix.size(); c++)
swap(matrix[r][c], matrix[c][r]);
for (int i=0; i<matrix.size(); i++) {
int l = 0;
int r = matrix.size() - 1;
while (l<r) {
swap(matrix[i][l], matrix[i][r]);
l++;
r--;
}
}
}
};