八数码问题 IDA*搜索

#include<iostream>
#include<string>
#include<cmath>
#include<cstring>
#include<vector>
#include<map>
#include<set>
#include<algorithm>
#include<queue>
#include<stack>
#include<sstream>
#include<cstdio>
#define INF 0x3f3f3f3f
//const int maxn = 1e6 + 5;
const double PI = acos(-1.0);
typedef long long ll;
using namespace std;

char ss[15];
int ans[4][4] = {
    {0,0,0,0},
    {0,1,2,3},
    {0,8,0,4},
    {0,7,6,5}
};
int a[5][5];
int k, judge;
int dx[] = { 0,1,-1,0 };
int dy[] = { 1,0,0,-1 };

int check() {
    for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 3; j++) {
            if (ans[i][j] != a[i][j]) return 0;
        }
    }
    return 1;
}

int test(int step) {
    int cnt = 0;
    for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 3; j++) {
            if (ans[i][j] != a[i][j]) {
                if (++cnt + step > k) return 0;
            }
        }
    }
    return 1;
}

void A_star(int step, int x, int y, int pre) {
    if (step == k) {
        if (check()) judge = 1; return;
    }
    if (judge) return;
    for (int i = 0; i < 4; i++) {
        int xx = x + dx[i], yy = y + dy[i];
        if (xx < 1 || xx>3 || yy < 1 || yy>3 || pre + i == 3) continue;
        swap(a[x][y], a[xx][yy]);
        if (test(step) && !judge) A_star(step + 1, xx, yy, i);
        swap(a[x][y], a[xx][yy]);
    }
}

int main() {
    int x, y;
    scanf("%s",ss);
    for (int i = 0; i < 9; i++) {
        a[i / 3 + 1][i % 3 + 1] = ss[i] - '0';
        if (ss[i] - '0' == 0) x = i / 3 + 1, y = i % 3 + 1;
    }
    if (check()) {
        printf("0\n");
    }
    else {
        while (++k) {
            A_star(0, x, y, -1);
            if (judge) {
                printf("%d", k);
                break;
            }
        }
    }
    return 0;
}