lintcode:Rotate Image Show result

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本文介绍了一种在不使用额外空间的情况下，将n x n的二维矩阵顺时针旋转90度的方法。

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You are given an n x n 2D matrix representing an image. Rotate the image by 90 degrees (clockwise).

Example

Given a matrix

[
    [1,2],
    [3,4]
]

rotate it by 90 degrees (clockwise), return

[
    [3,1],
    [4,2]
]

Challenge

Do it in-place.

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class Solution {
public:
    /**
     * @param matrix: A list of lists of integers
     * @return: Void
     */
    void rotate(vector<vector<int> > &matrix) {
        // write your code here
        
        if (matrix.size() == 0 || matrix.size() == 1)
            return;
            
        int layer = matrix.size()/2;
        
        for (int layer=0; layer<matrix.size()/2; layer++)
        {
            int first = layer;
            int last  = matrix.size()-1-layer;
            
            for (int i=first; i<last; i++)
            {
                int offset = i-first;
                
                int top = matrix[first][i];
                
                matrix[first][i] = matrix[last-offset][first];
                matrix[last-offset][first] = matrix[last][last-offset];
                matrix[last][last-offset] = matrix[i][last];
                matrix[i][last] = top;
            }
        }
    }
};