【题解】P2324 [SCOI2005]骑士精神

·有关IDA*

是带有估值函数的迭代加深搜索，表现出出色的效率。

估值函数可以简单的定义为「已经到位的骑士的个数」。

然后就是普通的迭代加深了。

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算法酷炫不一定赢，搜索好才是成功。

——Loli

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Code：

#include <iostream>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <fstream>
#define re register
#define GC getchar()
#define Clean(X,K) memset(X,K,sizeof(X))
#define Jud(X,Y) (X<0||X>=N||Y<0||Y>=N)
using namespace std ;
int Qread () {
    int X =  ;
    char C = GC ;
    while (C > '' || C < '') C = GC ;
    while (C >='' && C <='') {
        X = X *  + C - '' ;
        C = GC ;
    }
    return X ;
}
const int Dx[] = {,,-,-,,,-,-},Dy[] = {,-,,-,,-,,-},N =  , Aim[N + ][N + ] = {
    {,,,,,-},
    {,,,,,-},
    {,,,,,-},
    {,,,,,-},
    {,,,,,-},
    {-,-,-,-,-,-}
};
int A[N + ][N + ] , Sx , Sy ;
int G () {
    int Ans =  ;
    for (re int i =  ; i < N; ++ i) for (re int j =  ; j < N; ++ j) if (A[i][j] != Aim[i][j]) ++ Ans ;
    return Ans ;
}
int Ans , Fl =  ;
void DFS (int X , int Y , int Stp) {
    int Star = G() ;
    if (Stp + Star > Ans + ) return ;
    if (Fl) return ;
    if (Star == ) {
        Fl =  ;
        return ;
    }
    for (re int i =  ; i <  ;++ i) {
        int Tx = Dx[i] + X , Ty = Dy[i] + Y ;
        if (Jud(Tx , Ty)) continue ;
        swap(A[X][Y] , A[Tx][Ty]) ;
        DFS (Tx , Ty , Stp + ) ;
        swap (A[X][Y] , A[Tx][Ty]) ;
    }
}
int main () {
//    freopen ("P2324.in" , "r" , stdin) ;
    int Times = Qread () ;
    while (Times -- ) {
        for (re int i =  ; i < N; ++ i) {
            for (re int j =  ; j < N; ++ j) {
                char C = GC ;
                while (C != '*' && C != '' && C != '') C = GC ;
                if (C == '') A[i][j] =  ;
                if (C == '') A[i][j] =  ;
                if (C == '*') {
                    A[i][j] =  ;
                    Sx = i , Sy = j ;
                }
            }
        }
        Fl =  ;
        for (Ans =  ; Ans <=  ; ++ Ans) {
            DFS (Sx , Sy , ) ;
            if (Fl)  {
                cout << Ans <<endl;
                break ;
            }
        }
        if (!Fl)cout << - <<endl;
    }
    fclose (stdin) , fclose (stdout) ;
    return  ;
}

Thanks！