内容简介:You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).Note:
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] ]
难度: medium
题目:给定n * n的矩阵表示一张图片。顺时针90度旋转。
注意:必须原地旋转不允许申请额外的空间。
思路:90度旋转有数学规律可寻。
Runtime: 1 ms, faster than 100.00% of Java online submissions for Rotate Image.
Memory Usage: 26.4 MB, less than 46.19% of Java online submissions for Rotate Image.
class Solution { public void rotate(int[][] matrix) { int n = matrix.length; int nIdx = n - 1; for (int i = 0; i < n / 2; i++) { int start = i; int end = nIdx - i; for (int j = start; j < end; j++) { int t = matrix[nIdx - j][i]; matrix[nIdx - j][i]= matrix[end][nIdx - j]; matrix[end][nIdx - j] = matrix[j][end]; matrix[j][end] = matrix[i][j]; matrix[i][j] = t; } } } }
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何海涛 / 电子工业出版社 / 2017-5 / 65.00
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