HDU-2259-Continuous Same Game (2)(BFS+DFS+模拟)

最新推荐文章于 2019-06-13 08:17:04 发布

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最新推荐文章于 2019-06-13 08:17:04 发布

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本文探讨了一种在面对复杂问题时改进的贪心策略与深度优先搜索方法的应用。通过实例分析，展示如何通过算法优化提升解决方案效率。详细介绍了算法设计、实现步骤及性能评估过程，旨在为解决实际问题提供新的思考角度。

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Problem Description

After repeated attempts, LL finds the greedy strategy is very awful in practice. Even there is no apparent evidence to proof it is better than a random one. So he has to drop this strategy and try to discover a better one.

Input

There are 100 test cases. Each test case begins with two integers n,m ( 5<=n,m<=20 ), which is the size of the board. Then n lines follow, each contains m characters, indicating the color of the block. There are 5 colors, and each with equal probability.

Output

For each test case, first output a single line containing the number of steps S. Then S lines follow, each contains two integers indicating the position of an arbitrary block of the group you want to remove.

For the i-th test case, let Ai is the total point of your scheme and Bi is the total point of the greedy strategy . Then I will calculate the average of (Ai/Bi), 1<=i<=100. You will get WA if your ouput is invalid or this average is less than 1.5.

Sample Input

Sample Output

5
2 2
0 0
1 1
2 1
4 4

Hint
35552    35000    00000    00000    00000    00000
31154    31552    05552    00002    00002    00000
33222    33154    01154    01104    00004    00000
21134    21134    21134    21134    20034    20030
12314    12314    12314    12314    12314    12312

The total point is 6+12+12+12+6=48.

思路：总体是用BFS搞的，消除格子的时候就用DFS。对每一个状态都求一个评估值val，用优先队列来维护，每次使评估值最大的元素出队，并且更新答案。题目不要求最优解，处理25次左右就可以满足题意了。

#include <cstdio>
#include <algorithm>
#include <queue>
using namespace std;

struct S{
char mp[20][21];
int step,ans,x[50],y[50],val;
int num[20][20];

bool operator<(const S &p) const
{
    return val<p.val;
}

}t,ans,tt;

int n,m,nxt[4][2]={{1,0},{0,1},{-1,0},{0,-1}},cnt;
char temp[20][21];
bool vis[20][20];

void dfs(int x,int y,char c)
{
    int i,j;

    for(i=0;i<4;i++)
    {
        x+=nxt[i][0];
        y+=nxt[i][1];

        if(x>=0 && x<n && y>=0 && y<m && !vis[x][y] && temp[x][y]==c)
        {
            vis[x][y]=1;

            cnt++;

            dfs(x,y,c);
        }

        x-=nxt[i][0];
        y-=nxt[i][1];
    }
}

void tran(int x,int y,char num,char (*d)[21])
{
    for(int i=0;i<4;i++)
    {
        x+=nxt[i][0];
        y+=nxt[i][1];

        if(x>=0 && x<n && y>=0 && y<m && d[x][y]==num)
        {
            d[x][y]='0';

            tran(x,y,num,d);
        }

        x-=nxt[i][0];
        y-=nxt[i][1];
    }
}

void move(char (*d)[21])
{
    int i,j,k;

    for(i=n-1;i>=0;i--)//向下移动
    {
        for(j=0;j<m;j++)
        {
            if(d[i][j]=='0')
            {
                for(k=i-1;k>=0;k--)
                {
                    if(d[k][j]>'0')
                    {
                        d[i][j]=d[k][j];
                        d[k][j]='0';

                        break;
                    }
                }
            }
        }
    }

    int t=m-1;
    while(t--)//向左移动，注意连续两列都为空的情况
    {
        for(j=0;j<m-1;j++)
        {
            for(i=0;i<n;i++) if(d[i][j]>'0') break;

            if(i==n)
            {
                for(i=0;i<n;i++)
                {
                    d[i][j]=d[i][j+1];

                    d[i][j+1]='0';
                }
            }
        }
    }
}

void eval(S &node)//评估
{
    int i,j;

    for(i=0;i<n;i++) for(j=0;j<m;j++) vis[i][j]=0,temp[i][j]=node.mp[i][j];

    node.val=node.ans;

    for(i=0;i<n;i++) for(j=0;j<m;j++)
    {
        node.num[i][j]=0;

        if(temp[i][j]>'0' && !vis[i][j])
        {
            vis[i][j]=1;

            cnt=1;

            dfs(i,j,temp[i][j]);

            if(cnt>1)
            {
                node.num[i][j]=cnt;

                node.val+=cnt*(cnt-1);
            }
        }
    }
}

int main()
{
    int i,j,p,q,tot;

    while(~scanf("%d%d",&n,&m))
    {
        for(i=0;i<n;i++) scanf("%s",t.mp[i]);

        t.step=0;
        t.ans=0;
        t.val=0;

        ans.ans=0;

        priority_queue<S>que;

        eval(t);

        que.push(t);

        tot=0;

        while(!que.empty())
        {
            t=que.top();

            if(t.ans>ans.ans) ans=t;//更新答案

            tot++;

            if(tot>24) break;//循环25次就退出

            que.pop();

            for(i=0;i<n;i++) for(j=0;j<m;j++)
            {
                if(t.num[i][j])
                {
                    tt=t;
                    
                    tran(i,j,t.mp[i][j],t.mp);//清除格子

                    t.mp[i][j]='0';

                    move(t.mp);//移动格子

                    t.x[t.step]=i;
                    t.y[t.step]=j;
                    t.step++;
                    t.ans+=t.num[i][j]*(t.num[i][j]-1);

                    eval(t);//重新评估

                    que.push(t);

                    t=tt;
                }
            }
        }

        printf("%d\n",ans.step);

        for(i=0;i<ans.step;i++) printf("%d %d\n",ans.x[i],ans.y[i]);
    }
}