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# LeetCode #48: Rotate Image (C/C++).

medium

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.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 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--; } } } };