The topic is from LeetCode
Other solutions or source code can be accessed: tongji4m3
description
Given an n × n two-dimensional matrix represents an image.
Rotate the image 90 degrees clockwise.
Description:
You have to rotate the image in place, which means you need to directly modify the input two-dimensional matrix. Please do not use another matrix to rotate the image.
Example 1:
给定 matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],
原地旋转输入矩阵,使其变为:
[
[7,4,1],
[8,5,2],
[9,6,3]
]
Example 2:
给定 matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],
原地旋转输入矩阵,使其变为:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]
Ideas
In the peripheral rotation, you only need to rotate [0,0], to [0,n-2] and the corresponding four corners in turn.
Because it is a square matrix, we define lo and hi to represent the upper layer of traversal and the lower layer of traversal. , And also useful for left and right
detail
Code
public void rotate(int[][] matrix)
{
int lo = 0, hi = matrix.length - 1;
while(lo<hi)
{
for (int i = 0; i < hi - lo; i++)
{
int temp=matrix[lo][lo+i];
matrix[lo][lo + i] = matrix[hi - i][lo];
matrix[hi - i][lo] = matrix[hi][hi - i];
matrix[hi][hi - i] = matrix[lo + i][hi];
matrix[lo + i][hi] = temp;
}
++lo;
--hi;
}
}