【算法设计作业】week16

week16

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48. Rotate Image

来源:https://leetcode.com/problems/rotate-image/description/

题意

给定一个矩阵，输出顺时针旋转之后的矩阵

思路

最简单的思路是，建立每一个点与新店的数学关系，然后映射过去。
但是在discussion有人给出了顺时针旋转和逆时针旋转的算法，相当简洁。

参考代码

/* * 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]);    }}