[C ++ algorithm design] Eight Digital Problems

8. Digital question [question]: 1 ~ Place the eight square slide of 8 into three rows and three columns (a grid is empty). You can move the adjacent slide of the space to the space at a time, calculate the minimum number of steps that can move the target. If the target cannot be reached, the value is-1. [Analysis] We can define each situation as a "state", and each State is composed of nine lattice numbers in sequence, for example, the Left State is, 2, 4, 3, 0, 7, 8, 6, similarly, the right state is: 1, 2, 3, 4, 5, 6, 7, 8, 0. Then we can use the width-first traversal (BFS) method to expand a new state for each State, and then know that the target State is searched. [Code]

Typedef int State [9]; // defines the "State" type const int Maxstate = 1000000; State st [Maxstate], goal; // status array int dist [Maxstate]; // if you want to print the scheme, you also need to define a parent number array int fa [Maxstate]; const int dx [] = }; const int dy [] = {,-}; void init () {}// initialization function int bfs () {init (); int front = 1; int rear = 2; while (front <rear) {State & s = st [front]; if (memcmp (goal, s, sizeof (s) = 0) return front; int z; for (z = 0; z <9; z ++) if (! S [z]) break; int x = z/3, y = z % 3; for (int d = 0; d <4; d ++) {int newx = x + dx [d]; int newy = y + dy [d]; int newz = newx * 3 + newy; if (newx> = 0 & newx <3 & newy> = 0 & newy <3) {State & t = st [rear]; memcpy (& t, & s, sizeof (s); t [newz] = s [z]; t [z] = s [newz]; dist [rear] = dist [front] + 1; if (insert (rear) rear ++; // judge weight} front ++;} return 0 ;}

 

The above Code lacks a main () function, an init () function, and a judge-heavy insert () function. I think a more important point is to define the Statement of the "State" type, I started to think it was written like typedef int [9] State, but it was not correct. I don't know why it was written like that. It is easy to write errors. Then there is a lot of "references" in the most critical bfs function, which can be learned. This is very convenient and easier to understand than the pointer.