48. Rotate Image
答案二
这网友答案简直绝了…
/*
* clockwise rotate
* first reverse up to down, then swap the symmetry
* 1 2 3 7 8 9 7 4 1
* 4 5 6 => 4 5 6 => 8 5 2
* 7 8 9 1 2 3 9 6 3
*/
void rotate(vector<vector<int> > &matrix) {
reverse(matrix.begin(), matrix.end());
for (int i = 0; i < matrix.size(); ++i) {
for (int j = i + 1; j < matrix[i].size(); ++j)
swap(matrix[i][j], matrix[j][i]);
}
}
/*
* anticlockwise rotate
* first reverse left to right, then swap the symmetry
* 1 2 3 3 2 1 3 6 9
* 4 5 6 => 6 5 4 => 2 5 8
* 7 8 9 9 8 7 1 4 7
*/
void anti_rotate(vector<vector<int> > &matrix) {
for (auto vi : matrix) reverse(vi.begin(), vi.end());
for (int i = 0; i < matrix.size(); ++i) {
for (int j = i + 1; j < matrix[i].size(); ++j)
swap(matrix[i][j], matrix[j][i]);
}
}
答案二
private static void rotateBy90Degree(byte[][] matrix) {
reverseVertically(matrix);
reverseSymmetry(matrix);
}
private static void rotateBy180Degree(byte[][] matrix) {
reverseVertically(matrix);
reverseHorizontally(matrix);
}
private static void rotateBy270Degree(byte[][] matrix) {
reverseHorizontally(matrix);
reverseSymmetry(matrix);
}
private static void reverseVertically(byte[][] matrix) {
for (int i=0; i<matrix.length/2; i++) {
byte[] tempLine = matrix[i];
matrix[i] = matrix[matrix.length - i - 1];
matrix[matrix.length - i - 1] = tempLine;
}
}
private static void reverseHorizontally(byte[][] matrix) {
for (int i=0; i<matrix.length; i++) {
for (int j=0; j<matrix[i].length/2; j++) {
byte temp = matrix[i][j];
matrix[i][j] = matrix[i][matrix[i].length - 1 - j];
matrix[i][matrix[i].length - 1 - j] = temp;
}
}
}
private static void reverseSymmetry(byte[][] matrix) {
for (int i=0; i<matrix.length; i++) {
for (int j=i+1; j<matrix[i].length; j++) {
byte temp = matrix[i][j];
matrix[i][j] = matrix[j][i];
matrix[j][i] = temp;
}
}
}