[leetcode]Rotate Image

问题描述：

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

基本思路：

此题要求矩阵顺时针转90度。可以找出元素选择规律：

i‘ = j;

j' = n-1-i;

i,j 位置的元素旋转后应该到i',j'位置。

最基本的解法可以借助与一个副本matrix。如不不利用副本，可以将对位位置的四个元素一个一个的替换。具体请结合代码查看。

代码：

    void rotate(vector<vector<int> > &matrix) {        int n = matrix.size();                int low = 0,high = n-1,j = 0;        while(low < high){            int tmpi,tmpj,value1,value2,tmp_i,tmp_j;            for(int i = low ; i < high; i++){                //1                tmp_i = i;                tmp_j = j;                tmpi = tmp_j;                tmpj = n-1-tmp_i;                value1 = matrix[tmpi][tmpj];                matrix[tmpi][tmpj] =matrix[i][j];                //2                tmp_i = tmpi;                tmp_j = tmpj;                tmpi = tmp_j;                tmpj = n-1-tmp_i;                value2= value1;                value1 = matrix[tmpi][tmpj];                matrix[tmpi][tmpj] =value2;                                //3                tmp_i = tmpi;                tmp_j = tmpj;                tmpi = tmp_j;                tmpj = n-1-tmp_i;                value2 = value1;                value1 = matrix[tmpi][tmpj];                matrix[tmpi][tmpj] = value2;                                //4                tmp_i = tmpi;                tmp_j = tmpj;                tmpi = tmp_j;                tmpj = n-1-tmp_i;                value2 =value1;                value1 = matrix[tmpi][tmpj];                matrix[tmpi][tmpj] = value2;            }            low++;            high--;            j++;        }    }