rotate matrix

clockwise 90 degrees.

m
00 01 02 03
10 11 12 13
20 21 22 23
30 31 32 33

// right = top
00 01 02 03
         13
         23

rotate90C(m):
    // no throw for n = 0
    if m == null || 
        (m.length() > 0 && m.length() != m[0].length()):
        throw
    n = m.length()
    for layer = 0, layer < n/2, layer++:
        for i = layer, i < n-1 -layer, i++:
            // temp = top
            temp = m[layer][i]
            // top = left
            m[layer][i] = m[n-1-i][layer]
            // left = bottom
            m[n-1-i][layer] = m[n-1-layer][n-1-i]
            // bottom = right
            m[n-1-layer][n-1-i] = m[i][n-1-layer]
            // right = temp
            m[i][n-1-layer] = temp

[Hat tip to ctci]

180 degrees.

rotate180(m):
    // no throw for n = 0
    if m == null || 
        (m.length() > 0 && m.length() != m[0].length()):
        throw
    for layer = 0, layer < n/2, layer++:
        for i = layer, i < ni -layer, i++:
            // top - bottom
            swap(m, layer, i, ni -layer, ni -i)
            // left - right
            swap(m, i, ni -layer, ni -i, layer)