给定一个n*n的二维向量，顺时针旋转90度

class Solution {
public:
    void rotate(vector<vector<int> > &matrix) {
        int length = matrix.size();
        for (int i = 0; i < length/2; i++)
        {
            for (int j = i; j < length  - i - 1; j++)
            {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[length - j - 1][i];
                matrix[length - j - 1][i] = matrix[length - i - 1][length - j - 1];
                matrix[length - i - 1][length - j - 1] = matrix[j][length - i - 1];
                matrix[j][length - i - 1] = tmp;
            }
        }
    }
};

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原文：http://www.cnblogs.com/flyjameschen/p/5d92c59daba1cc6b261b48be661bd118.html