README_EN.md

48. Rotate Image

中文文档

Description

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.

 

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]]

Example 3:

Input: matrix = [[1]]
Output: [[1]]

Example 4:

Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]

 

Constraints:

• matrix.length == n
• matrix[i].length == n
• 1 <= n <= 20
• -1000 <= matrix[i][j] <= 1000

Solutions

Python3

class Solution:
    def rotate(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        s, n = 0, len(matrix)
        while s < (n >> 1):
            e = n - s - 1
            for i in range(s, e):
                t = matrix[i][e]
                matrix[i][e] = matrix[s][i]
                matrix[s][i] = matrix[n - i - 1][s]
                matrix[n - i - 1][s] = matrix[e][n - i - 1]
                matrix[e][n - i - 1] = t
            s += 1

Java

class Solution {
    public void rotate(int[][] matrix) {
        int s = 0, n = matrix.length;
        while (s < (n >> 1)) {
            int e = n - s - 1;
            for (int i = s; i < e; ++i) {
                int t = matrix[i][e];
                matrix[i][e] = matrix[s][i];
                matrix[s][i] = matrix[n - i - 1][s];
                matrix[n - i - 1][s] = matrix[e][n - i - 1];
                matrix[e][n - i - 1] = t;
            }
            ++s;
        }
    }
}

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