Studio10_inclass

function rotate_matrix(M) {
    const n = array_length(M);  // M is assumed n x n.
    function swap(r1, c1, r2, c2) {
        const temp = M[r1][c1];
        M[r1][c1] = M[r2][c2];
        M[r2][c2] = temp;
    }

    for(let i = 0; i < n; i = i + 1){
        for(let j = i; j < n; j = j + 1 ){
            swap(i, j, j, i); // transpose
        }
        
        for(let j = 0; j < math_floor(n/2); j = j + 1 ){
            swap(i, j, i, n-j-1); // reverse
        }
        
    }
  
}

const M =
[[ 1,  2,  3,  4],
 [ 5,  6,  7,  8],
 [ 9, 10, 11, 12],
 [13, 14, 15, 16]];
 
rotate_matrix(M);
M;

// M should have become
// [[13,  9, 5, 1], 
//  [14, 10, 6, 2], 
//  [15, 11, 7, 3], 
//  [16, 12, 8, 4]]

/*

Indices

[[(0,0), (0,1), (0,2), (0,3)]
 [(1,0), (1,1), (1,2), (1,3)]
 [(2,0), (2,1), (2,2), (2,3)]
 [(3,0), (3,1), (3,2), (3,3)]]
 
[[(0,0), (1,0), (2,0), (3,0)]
 [(0,1), (1,1), (2,1), (3,1)]
 [(0,2), (1,2), (2,2), (3,2)]
 [(0,3), (1,3), (2,3), (3,3)]] 
 
*/