https://leetcode.com/problems/reshape-the-matrix

function matrixReshape(mat: number[][], r: number, c: number): number[][] {
    const total = mat.length * mat[0].length;
    if (total !== r*c) return mat;

    return Array.from({ length: r }).map((_, i) =>
        Array.from({ length: c}).map((__, j) => {
            const ix = c*i + j;
            const oi = Math.floor(ix / mat[0].length);
            const oj = ix % mat[0].length;
            return mat[oi][oj];
        })
    );
};