题目描述

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样例

blablabla

算法1

(暴力枚举) $O(n^2)$

blablabla

时间复杂度

参考文献

C++ 代码

#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <queue>

using namespace std;

int bfs(string state)
{
    queue<string> q;
    unordered_map<string, int> d;

    q.push(state);
    d[state] = 0;

    int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

    string end = "12345678x";
    while (q.size())
    {
        auto t = q.front();
        q.pop();

        if (t == end) return d[t];

        int distance = d[t];
        int k = t.find('x');
        int x = k / 3, y = k % 3;//字符串x在二维表状态时的坐标 
        for (int i = 0; i < 4; i ++ )
        {
            int a = x + dx[i], b = y + dy[i];
            if (a >= 0 && a < 3 && b >= 0 && b < 3)
            {
                swap(t[a * 3 + b], t[k]);
                if (!d.count(t))
                {
                    d[t] = distance + 1;
                    q.push(t);
                }
                swap(t[a * 3 + b], t[k]);
            }
        }
    }

    return -1;
}

int main()
{
    freopen("845.in","r",stdin); 
    char s[2];

    string state;
    for (int i = 0; i < 9; i ++ )
    {
        cin >> s;
        state += *s;
    }

    cout << bfs(state) << endl;

    return 0;
}

算法2

(暴力枚举) $O(n^2)$

blablabla

时间复杂度

参考文献

C++ 代码

blablabla