1085: [SCOI2005]骑士精神

IDA*

A*部分：每次判断当前使用步数和至少还需步数的和是否满足当前解；

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
 
using namespace std;
 
int T, dep;
 
bool esp;
 
bool tgt[6][6] = {
    {1,1,1,1,1},
    {0,1,1,1,1},
    {0,0,0,1,1},
    {0,0,0,0,1},
    {0,0,0,0,0}
};
 
int dir[8][2] = {
    1,2,1,-2,-1,2,-1,-2,2,1,2,-1,-2,1,-2,-1
};
 
bool judge(bool nmp[6][6], int x, int y) {
    if (x != 2 || y != 2) return false;
    for (int i = 0; i < 5; ++i) {
        for (int j = 0; j < 5; ++j) 
            if (nmp[i][j] != tgt[i][j])
                return false;
    }
    return true;
}
 
int minstep(bool nmp[6][6], int step) {
    int otherstep = 0;
    for (int i = 0; i < 5; ++i) {
        for (int j = 0; j < 5; ++j) 
            if (nmp[i][j] != tgt[i][j]) 
                otherstep ++;
                if (otherstep + step > dep)
                    return false;
    }
    return true;
}
 
void dfs(int step, bool nmp[6][6], int x, int y) {
    if (step == dep) {
        if (judge(nmp, x, y)) esp = true;
        return ;
    }
    if (esp) return ;
    for (int i = 0; i < 8; ++i) {
        int nx = x + dir[i][0];
        int ny = y + dir[i][1];
        if (nx < 0 || nx >= 5 || ny < 0 || ny >= 5) continue;
        swap(nmp[x][y], nmp[nx][ny]);
        if (minstep(nmp, step)) dfs(step+1, nmp, nx, ny);
        swap(nmp[x][y], nmp[nx][ny]);
    }
}
 
int main() {
    scanf("%d", &T);
    for (int cas = 1; cas <= T; ++cas) {
        esp = false;
        bool nmp[6][6];
        memset(nmp, 0, sizeof(nmp));
        int x, y;
        for (int i = 0; i < 5; ++i) {
            char c[7];
            scanf("%s", c);
            for (int j = 0; j < 5; ++j) {
                if (c[j] == '*') {x = i, y = j;}
                else nmp[i][j] = c[j] - '0';
            }
        }
        for (dep = 1; dep <= 15; ++dep) {
            dfs(0, nmp, x, y);
            if (esp) {
                printf("%d\n", dep);
                break;
            }
        }
        if (!esp) printf("-1\n");
    }
    return 0;
}