USACO 3.2.5 Magic Squares (康托hash + BFS) - 小阮的菜田 - C++博客

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USACO 3.2.5 Magic Squares (康托hash + BFS)

康托hash + BFS

/*

ID: lorelei3

TASK: msquare

LANG: C++

*/

#include <fstream>

#include <memory.h>

#include <algorithm>

#include <functional>

#include <queue>

using namespace std;

const int MAX = 40330;

typedef struct {

int hash;

int str[10];

char op;

int pre;

int index;

}Node;

Node nodes[MAX];

bool used[MAX];

int fac[10];

int dest[10];

int target,cnt;

char ops[MAX];

int cantor_hash(int a[]){

int ans=0;

bool in[10];

memset(in, false, 10);

for(int i=0; i<8; ++i){

int k=a[i];

in[k]=true;

int tmp =k;

for(int j=1; j<k; ++j)

if(in[j])

--tmp;

--tmp;

ans+=fac[7-i]*tmp;

}

return ans+1;

}

void init(){

memset(used, false, sizeof(used));

for(int i=0; i<8; ++i)

nodes[cnt].str[i] = i+1;

int k;

fac[0]=fac[1]=1;

for(k=2; k<10; ++k)

fac[k] = k*fac[k-1];

}

void change(int a[]){

for(int i=0; i<4; ++i){

int tmp = a[i];

a[i] = a[7-i];

a[7-i] = tmp;

}

}

void insert(int a[]){

int i,tmp;

tmp = a[3];

for(i=2; i>=0; --i)

a[i+1] = a[i];

a[0] = tmp;

tmp = a[4];

for(i=5; i<8; ++i)

a[i-1] = a[i];

a[7] = tmp;

}

void rotate(int a[]){

int tmp;

tmp=a[1];

a[1]=a[6];

a[6]=tmp;

tmp=a[2];

a[2]=a[5];

a[5]=tmp;

tmp=a[2];

a[2]=a[6];

a[6]=tmp;

}

void bfs(){

int v, top;

Node tmp;

queue<int> Q;

cnt=0;

nodes[cnt].hash = cantor_hash(nodes[cnt].str);

nodes[cnt].index = 0;

nodes[cnt].pre = -1;

used[nodes[cnt].hash] = true;

Q.push(cnt);

while(!Q.empty()){

top = Q.front();

Q.pop();

tmp = nodes[top];

change(tmp.str);

v = cantor_hash(tmp.str);

if(!used[v]){

cnt++;

used[v] = true;

tmp.op = 'A';

tmp.hash = v;

tmp.pre = nodes[top].index;

tmp.index = cnt;

nodes[cnt] = tmp;

Q.push(cnt);

}

if(v==target)

break;

tmp = nodes[top];

insert(tmp.str);

v = cantor_hash(tmp.str);

if(!used[v]){

cnt++;

used[v] = true;

tmp.op = 'B';

tmp.hash = v;

tmp.pre = nodes[top].index;

tmp.index = cnt;

nodes[cnt] = tmp;

Q.push(cnt);

}

if(v==target)

break;

tmp = nodes[top];

rotate(tmp.str);

v = cantor_hash(tmp.str);

if(!used[v]){

cnt++;

used[v] = true;

tmp.op = 'C';

tmp.hash = v;

tmp.pre = nodes[top].index;

tmp.index = cnt;

nodes[cnt] = tmp;

Q.push(cnt);

}

if(v==target)

break;

}

}

int main(){

int i;

ifstream fin("msquare.in");

ofstream fout("msquare.out");

for(i=0; i<8; ++i)

fin>>dest[i];

init();

target = cantor_hash(dest);

if(target == cantor_hash(nodes[0].str)){

fout<<0<<endl<<endl;

return 0 ;

}

bfs();

int count=-1, t=cnt;

while(t!=-1){

ops[++count] = nodes[t].op;

t = nodes[t].pre;

}

reverse(ops, ops+count);

fout<<count<<endl<<ops<<endl;

return 0;

}

posted on 2010-12-30 23:32 小阮阅读(264) 评论(0) 编辑收藏引用所属分类: USACO

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