Reshape the Matrix问题及解法

问题描述：

In MATLAB, there is a very useful function called 'reshape', which can reshape a matrix into a new one with different size but keep its original data.

You're given a matrix represented by a two-dimensional array, and two positive integers r and c representing
the row number and column number of the wanted reshaped matrix, respectively.

The reshaped matrix need to be filled with all the elements of the original matrix in the same row-traversing order as they were.

If the 'reshape' operation with given parameters is possible and legal, output the new reshaped matrix; Otherwise, output the original matrix.

示例：

Input:
nums =
[[1,2],
[3,4]]
r = 1, c = 4
Output:
[[1,2,3,4]]
Explanation:
The row-traversing of nums is [1,2,3,4]. The new reshaped matrix is a 1 * 4 matrix,
fill it row by row by using the previous list.

Input:
nums =
[[1,2],
[3,4]]
r = 2, c = 4
Output:
[[1,2],
[3,4]]
Explanation:
There is no way to reshape a 2 * 2 matrix to a 2 * 4 matrix. So out
4000
put the original matrix.

问题分析：
矩阵变换前后元素数量首先不能发生变化，再就是，我们可以在线性时间内利用整除求解答案。

class Solution {
public:
vector<vector<int> > matrixReshape(vector<vector<int> >& nums, int r, int c) {
int m = nums.size(), n = nums[0].size(), o = m * n;
if (r * c != o) return nums;
vector<vector<int> > res(r, vector<int>(c, 0));
for (int i = 0; i < o; i++) res[i / c][i % c] = nums[i / n][i % n];
return res;
}
};