【LeetCode】16.Rotate Image

题目描述(Medium)

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.

题目链接

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

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]
]

算法分析

方法一：先水平翻转，再对角线翻转；

方法二：先副对角线翻转，再水平翻转。

提交代码：

class Solution {
public:
	// 先水平翻转,再对角线翻转
	void rotate(vector<vector<int>>& matrix) {
		const int n = matrix.size();

		//水平翻转
		for (int i = 0; i < n / 2; ++i)
			for (int j = 0; j < n; ++j)
				swap(matrix[i][j], matrix[n - 1 - i][j]);

		//对角线翻转
		for (int i = 0; i < n; ++i)
			for (int j = i + 1; j < n; ++j)
				swap(matrix[i][j], matrix[j][i]);
	}
};

测试代码：

// ====================测试代码====================
void Test(const char* testName, vector<vector<int>>& matrix, vector<vector<int>>& expected)
{
	if (testName != nullptr)
		printf("%s begins: \n", testName);

	Solution s;
	s.rotate(matrix);

	if (matrix == expected)
		printf("passed\n");
	else
		printf("failed\n");

}

int main(int argc, char* argv[])
{
	vector<vector<int>> matrix = {
		{1, 2, 3},
		{4, 5, 6},
		{7, 8, 9}
	};
	vector<vector<int>> expected = {
		{7, 4, 1},
		{8, 5, 2},
		{9, 6, 3}
	};
	Test("Test1", matrix, expected);


	matrix = {
		{5, 1, 9, 11},
		{2, 4, 8, 10 },
		{13, 3, 6, 7 },
		{15, 14, 12, 16 }
	};
	expected = {
		{15, 13, 2, 5 },
		{14, 3, 4, 1 },
		{12, 6, 8, 9 },
		{16, 7, 10, 11 }
	};
	Test("Test2", matrix, expected);

	return 0;
}