Reshape thee Matrix

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.

Example 1: 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.

Example 2: 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 output the original matrix.

Solution: Convert matrix to one row

The simplest method is to extract all the elements of the given matrix by reading the elements in a row-wise fashion. In this implementation, we use a queue to put the extracted elements. Then, we can take out the elements of the queue formed in a serial order and arrange the elements in the resultant required matrix in a row-by-row order again.

vector<vector<int>> matrixReshape(vector<vector<int>>& nums, int r, int c) {
    if (nums.size() * nums[0].size() != r * c) return nums;

    vector<int> temp;
    for (int i=0; i<nums.size(); i++) {
        for (int j=0; j<nums[0].size(); j++) {
            temp.push_back(nums[i][j]);
        }
    }

    vector<vector<int>> newNums;
    for (int i=0; i<r; i++) {
        vector<int> rowVec;
        for (int j=0; j<c; j++) {
            rowVec.push_back(temp[i*c + j]);
        }
        newNums.push_back(rowVec);
    }
    return newNums;
}

Solution: Without using extra Space

Instead of unnecessarily using the queue as in the brute force approach, we can keep putting the numbers in the resultant matrix directly while iterating over the given matrix in a row-by-row order. While putting the numbers in the resultant array, we fix a particular row and keep on incrementing the column numbers only till we reach the end of the required columns indicated by cc. At this moment, we update the row index by incrementing it and reset the column index to start from 0 again. Thus, we can save the space consumed by the queue for storing the data that just needs to be copied into a new array.