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| #include <iostream>
#include <cstdio>
#include <queue>
#include <unordered_set>
using namespace std;
typedef pair <string, int> PSI;
const string ed = "123804765";
const int dx[4] = { 1, -1, 0, 0 },
dy[4] = { 0, 0, 1, -1 };
queue <PSI> q;
unordered_set <string> vis;
bool inside (int x, int y)
{
return x >= 0 && x < 3 && y >= 0 && y < 3;
}
void bfs ()
{
while (!q.empty())
{
PSI t = q.front();
q.pop();
if (t.first == ed)
{
cout << t.second;
return;
}
t.second++;
int x, y;
for (int i = 0; i < t.first.size(); i++)
if (t.first[i] == '0')
{
x = i / 3;
y = i % 3;
break;
}
for (int i = 0; i < 4; i++)
{
int nx = x + dx[i],
ny = y + dy[i];
if (!inside(nx, ny))
continue;
swap(t.first[x * 3 + y], t.first[nx * 3 + ny]);
if (!vis.count(t.first))
{
q.push(t);
vis.insert(t.first);
}
swap(t.first[x * 3 + y], t.first[nx * 3 + ny]);
}
}
}
int main ()
{
string t;
cin >> t;
q.push(make_pair(t, 0));
bfs();
return 0;
}
|