A*算法
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>
#include <unordered_map>
using namespace std;
typedef pair<int, string> P;
typedef string str;
int f(str st)
{
int res = 0;
for (int i = 0; i < st.size(); i ++ )
if (st[i] != 'x')
{
int t = st[i] - '1';
res += abs(i / 3 - t / 3) + abs(i % 3 - t % 3);
}
return res;
}
int Astar(str start)
{
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
char op[4] = {'u', 'r', 'd', 'l'};
str end = "12345678x";
unordered_map<str, int> dist;
unordered_map<str, pair<str, char>> prev;
priority_queue<P, vector<P>, greater<> > heap;
heap.push({0, start});
dist[start] = 0;
while (heap.size())
{
auto t = heap.top(); heap.pop();
str state = t.second;
if(state == end) break ;
int x, y;
for (int i = 0; i < state.size(); i ++ )
if (state[i] == 'x')
{
x = i / 3, y = i % 3;
break ;
}
str backup = state;
int step = dist[state];
for (int i = 0; i < 4; i ++ )
{
int a = x + dx[i], b = y + dy[i];
if (a < 0 || a > 2 || b < 0 || b > 2) continue ;
swap(state[x * 3 + y], state[a * 3 + b]);
if(!dist.count(state) || dist[state] > step + 1)
{
dist[state] = step + 1;
heap.push({dist[state] + f(state), state});
prev[state] = {backup, op[i]};
}
state = backup;
}
}
return dist[end];
}
int main()
{
str g, c, seq;
while (cin >> c)
{
g += c;
if (c != "x") seq += c;
}
int t = 0;
for (int i = 0; i < seq.size(); i ++ )
for (int j = i + 1; j < seq.size(); j ++ )
t += (seq[i] > seq[j]);
if (t & 1) printf("-1\n");
else cout << Astar(g) << endl;
return 0;
}