Reshape the Matrix

In MATLAB, there is a handy function called reshape which can reshape an m x n matrix into a new one with a different size r x c keeping its original data.

You are given an m x n matrix mat and two integers r and c representing the number of rows and the number of columns of the wanted reshaped matrix.

The reshaped matrix should 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.

LeetCode Problem - 566

class Solution {
    public int[][] matrixReshape(int[][] mat, int r, int c) {
        // Get the number of rows and columns in the original matrix
        int rows = mat.length;
        int col = mat[0].length;

        // If the total number of elements doesn't match between the original and reshaped matrices, return the original matrix
        if((rows * col) != (r * c)) return mat;

        // Step 1: Flatten the original matrix into a list
        List<Integer> list = new ArrayList<>();
        for(int i = 0; i < mat.length; i++){
            for(int j = 0; j < mat[0].length; j++){
                list.add(mat[i][j]); // Add each element of the matrix to the list
            }
        }

        // Step 2: Create the reshaped matrix with r rows and c columns
        int[][] ans = new int[r][c];
        int idx = 0; // Index to track elements in the list

        // Step 3: Fill the reshaped matrix with elements from the list
        for(int i = 0; i < r; i++){
            for(int j = 0; j < c; j++){
                ans[i][j] = list.get(idx); // Assign elements from the list to the reshaped matrix
                idx++; // Move to the next element in the list
            }
        }

        // Return the reshaped matrix
        return ans;
    }
}