48.rotate-image.cpp

/*
 * @lc app=leetcode id=48 lang=cpp
 *
 * [48] Rotate Image
 *
 * https://leetcode.com/problems/rotate-image/description/
 *
 * algorithms
 * Medium (47.14%)
 * Total Accepted:    230.8K
 * Total Submissions: 489.5K
 * Testcase Example:  '[[1,2,3],[4,5,6],[7,8,9]]'
 *
 * You are given an n x n 2D matrix representing an image.
 * 
 * Rotate the image by 90 degrees (clockwise).
 * 
 * Note:
 * 
 * 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.
 * 
 * Example 1:
 * 
 * 
 * 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]
 * ]
 * 
 * 
 * Example 2:
 * 
 * 
 * Given input matrix =
 * [
 * ⁠ [ 5, 1, 9,11],
 * ⁠ [ 2, 4, 8,10],
 * ⁠ [13, 3, 6, 7],
 * ⁠ [15,14,12,16]
 * ], 
 * 
 * rotate the input matrix in-place such that it becomes:
 * [
 * ⁠ [15,13, 2, 5],
 * ⁠ [14, 3, 4, 1],
 * ⁠ [12, 6, 8, 9],
 * ⁠ [16, 7,10,11]
 * ]
 * 
 * 
 */
class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        if(matrix.size() < 0)
            return;
        int n = matrix.size();
        for(int x = 0; x < n-1; ++x){
            for(int y = 0; y <= x && y < n-1-x; ++y){
                int temp = matrix[y][x];
                //cout << temp << "|";
                matrix[y][x] = matrix[n-1-x][y];
                matrix[n-1-x][y] = matrix[n-1-y][n-1-x];
                matrix[n-1-y][n-1-x] = matrix[x][n-1-y];
                matrix[x][n-1-y] = temp;
            }
        }
    }
};