POJ 3460 IDA*

    #include <cstdio>
    #include <cstring>
    #include <iostream>
    #include <cmath>
    using namespace std;
    int ans_flag = 0,n,case_num;
    int book_shell[20];
//H函数为某一个值后继值错位的个数：1的后继值为2，如果1的后继值不为2，则表示错位。进行一次交换只能改变三个值的后继值,i-1,j,k
    int H(int book[])
    {
        int sum = 0;
        for(int i = 0;i<n-1;i++)
        {
            if(book[i+1] != book[i]+1)
                sum++;
        }
        if(book[n-1] != n)
            sum++;
        return ceil(((double)sum/3));
    }

    //书籍交换 把[i,j]的书 和 [j+1,k]的书交换
    void Book_swap(int book[],int s,int m,int e)
    {
        int tmp[20],tmp_index = s;
        for(int i = m+1;i<=e;i++,tmp_index++)
            tmp[tmp_index] = book[i];

        for(int i = s;i<= m;i++,tmp_index++)
            tmp[tmp_index] = book[i];

        for(int i = s;i<=e;i++)
            book[i] = tmp[i];
    }

    void dfs(int step,int maxdp,int book[])
    {
        int h = H(book);
        if(h + step > maxdp || ans_flag == 1)return ;
        if(h == 0){
        printf("%d\n",step);
        ans_flag = 1;
        return ;
        }

        for(int i = 0;i<n-1;i++)
        {
            for(int j= i;j<n-1;j++)
            {
                for(int k = j+1;k<n;k++)
                {
                    if(book[j]+1 == book[j+1])continue;  //三个剪枝，从110ms到47ms
                    if(i>0&&book[i-1]+1 == book[i])continue;
                    if(k<n-1&&book[k]+1 == book[k+1])continue;
                    Book_swap(book,i,j,k);
                    dfs(step+1,maxdp,book);
                    if(ans_flag)return ;
                    Book_swap(book,i,i + k - j - 1,k); //恢复原来的
                }
            }
        }
    }

    void IDA()
    {
        int maxdp = 1;
        ans_flag = 0;
        while(1)
        {
            dfs(0,maxdp,book_shell);
            if(ans_flag)break;
            maxdp++;
            if(maxdp > 4)
            {
                printf("5 or more\n");
                break;
            }
        }
    }

    int main()
    {
        scanf("%d",&case_num);
        while(case_num--)
        {
            scanf("%d",&n);
            for(int i = 0;i<n;i++)
            {
                scanf("%d",&book_shell[i]);
            }
            IDA();
        }
        return 0;
    }