Rotate Image
You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Follow up: Could you do this in-place?
先按主对角线反转，再按垂直中轴线反转。
public class Solution {
public void rotate(int[][] matrix) {
int n = matrix[0].length;
int temp;
//先按主对角线反转,相当于矩阵转置(matrix transpose)
for(int i = 0; i < n; i++){
for(int j = i+1; j < n; j++){
temp = matrix[i][j];
matrix[i][j] = matrix[j][i];
matrix[j][i] = temp;
}
}
//再按垂直中轴线反转
for(int i = 0; i < n; i++){
for(int j = 0; j < n/2; j++){
temp = matrix[i][j];
matrix[i][j] = matrix[i][n-1-j];
matrix[i][n-1-j] = temp;
}
}
}
}
解法2 Matrix Rotation and Matrix Transpose
/*
* Method to get transpose of a matrix. It creates a new matrix to copy the
* elements because the physical structure of the matrix may change as a
* part of the transpose operation in case its not a square matrix.
*/
public int[][] transpose(int[][] mat) {
if (mat == null)
return null;
int m = mat.length;
int n = mat[0].length;
int[][] matResult = new int[n][m];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
matResult[j][i] = mat[i][j];
}
}
return matResult;
}
/*
* Method to get the horizontal reflection of the matrix.
*/
public void horizontalReflection(int[][] mat) {
int m = mat.length;
int n = mat[0].length;
int temp = 0;
for (int i = 0; i < m / 2; i++) {
for (int j = 0; j < n; j++) {
temp = mat[i][j];
mat[i][j] = mat[m - (i + 1)][j];
mat[m - (i + 1)][j] = temp;
}
}
}
/*
* Method to get the vertical reflection of the given matrix
*/
public void verticalReflection(int[][] mat) {
int m = mat.length;
int n = mat[0].length;
int temp = 0;
for(int i = 0; i < n; i++){
for(int j = 0; j < n/2; j++){
temp = mat[i][j];
mat[i][j] = mat[i][n-1-j];
mat[i][n-1-j] = temp;
}
}
}
/*
* Utility method to print the matrix.
*/
public void printMatrix(int[][] mat) {
int m = mat.length;
int n = mat[0].length;
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
System.out.print(mat[i][j] + " ");
}
System.out.println();
}
}