48. Rotate Image

題目

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.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] ]

解析

• 本題帶有技巧，如果允許申請空間，可以直接按列取，放入到新空間的一行即可

class Solution_48 { public:void rotate(vector<vector<int>>& matrix) {// 總的位置坐標關系：rotate[j][n-1-i]=a[i][j]int n = matrix.size();reverse(matrix.begin(), matrix.end()); //a[n-1-i][j]=a[i][j] for (int i = 0; i < n;i++){for (int j = i + 1; j < n;j++){swap(matrix[i][j],matrix[j][i]); // a[i][j]=a[j][i]}}return;} };

題目來源

• 48. Rotate Image
• 矩陣的操作-之前做過的

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