Skeleton sudoku, the second

Question

I've already set one skeleton Sudoku. Here's a rather harder one. (Nonetheless, it should be within the realms of what can be done by hand; I solved it manually myself to verify that there was only one solution. Actually, I got pretty good at solving these, because it took me something like 5 or 6 attempts to find a puzzle whose solution was unique, learning more each time about what sort of patterns would allow multiple solutions to exist…)

Here's the grid:

In case you can't see images: I shaded a1, b1, e1, d2, c3, e3, and c4.

And here are the rules (basically the same as before, but hopefully stated a bit more clearly):

• Following the grid lines, separate this puzzle into five contiguous regions of five squares each, and also place a digit from 0 to 4 inclusive in each square, so that:
  • (Generalised) Sudoku property:
    • Each horizontal row must contain one each of 0, 1, 2, 3, 4;
    • Each vertical column must contain one each of 0, 1, 2, 3, 4;
    • Each of your regions must contain one each of 0, 1, 2, 3, 4.
  • Palisade property:
    • Each shaded cell must contain a number equal to the number of edges of that cell which are region borders. (This is the same meaning that numbers have in a Slitherlink puzzle.)
    • Equivalently, the number on each shaded cell must be the number of adjacent cells that are either in a different region, or outside the map.

Answer 1

Looking at the first row, we can see that there are three blue squares, and blue squares on the edges are either 1, 2 or 3, so they must be 1 2 3 in some order. Furthermore, the middle one can be 1, so we have 2 1 3 or 3 1 2. Assuming 3 1 2, we eventually get here by placing forced numbers/walls:

Here we can notice it is impossible to settle the zeros in the bottom-left corner, as they would have to go at least two in the same region. So 3 1 2 is bad and we need 2 1 3:

A bit of "cheating" is now in order: we know this has a unique solution, so one of the blue squares is a 0 (otherwise, 0s and 4s would be completely interchangeable in the resulting sudoku). The only blue squares that can be a 0 are the ones not in the edges, and putting a 0 in the top two causes the top-right corner to be blocked, so the bottom most blue square is a 0. The 0 determines that entire region's shape, from where putting all of the other regions is now simple: