Google : Inplace rotate picture

Given an image represented by an NxN matrix, where each
pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

inplace就是不用额外空间的意思

先转换最外层，然后一层层内移到中心

void Rotate(int** pArr, int n, int nStep, int nLen)
{
        if (NULL == pArr || n <= 0 || nStep < 0 || nLen > n)
                return;

        if (0 == nLen || 1 == nLen) return;

        int i = nStep;
        for (int j = nStep; j < nStep+nLen-1; j++)
        {
                int nTmp = pArr[i][j];
                pArr[i][j] = pArr[j][n-1-i];
                pArr[j][n-1-i] = pArr[n-1-i][n-1-j];
                pArr[n-1-i][n-1-j] = pArr[n-1-j][i];
                pArr[n-1-j][i] = nTmp;
        }

        Rotate(pArr, n, nStep+1, nLen-2);
}

nTmp是不是也算额外空间...

可以先转置，然后再左右翻转。只需要用到swap，写起来很方便，不过交换的次数多些