深度优先搜索(dfs)
栈
广度优先搜索(bfs)
队列
记忆化搜索
搜索的剪枝
双向搜索
A*
IDA*(迭代加深搜索)
DLX
题目
bfs
#include <iostream>
#include <istream>
#include <sstream>
#include <vector>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <numeric>
#include <chrono>
#include <ctime>
#include <cmath>
#include <cctype>
#include <string>
#include <cstdio>
#include <iomanip>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <functional>
#include <iterator>
using namespace std;
const int target = 123804765, DIR[4][2] = {
{
1,0},{
-1,0},{
0,1},{
0,-1}};
pair<int, int> getZero(int n,vector<vector<int>> &arr) {
pair<int, int> ans(0, 0);
for (int i = 2; i >= 0; i--) {
for (int j = 2; j >= 0; j--) {
arr[i][j] = n % 10; n /= 10;
if (!arr[i][j]) {
ans.first = i;
ans.second = j;
}
}
}
return ans;
}
int getNum(vector<vector<int>>& arr) {
int ans = 0;
for (int i = 0; i <= 2; i++) {
for (int j = 0; j <= 2; j++) {
ans = ans * 10 + arr[i][j];
}
}
return ans;
}
int search(int start) {
int ans = 0;
vector<vector<int>> arr(3,vector<int>(3));
unordered_set<int> mmp;
mmp.insert(start);
queue<int> q;
q.push(start);
while (!q.empty()) {
int len = q.size();
for (int i = 0; i < len; i++) {
int top = q.front(); q.pop();
if (top == target) return ans;
pair<int, int> path = getZero(top, arr);
for (int j = 0; j < 4; j++) {
int nx = path.first + DIR[j][0];
int ny = path.second + DIR[j][1];
if (nx >= 0 && nx < 3 && ny >= 0 && ny < 3) {
swap(arr[path.first][path.second], arr[nx][ny]);
int num = getNum(arr);
if (!mmp.count(num)) {
mmp.insert(num);
q.push(num);
}
swap(arr[path.first][path.second], arr[nx][ny]);
}
}
}
++ans;
}
return -1;
}
int main()
{
int start;
cin >> start;
cout << search(start) << endl;
return 0;
}
双向bfs
#include <iostream>
#include <istream>
#include <sstream>
#include <vector>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <numeric>
#include <chrono>
#include <ctime>
#include <cmath>
#include <cctype>
#include <string>
#include <cstdio>
#include <iomanip>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <functional>
#include <iterator>
using namespace std;
const int target = 123804765, DIR[4][2] = {
{
1,0},{
-1,0},{
0,1},{
0,-1}};
pair<int, int> getZero(int n,vector<vector<int>> &arr) {
pair<int, int> ans(0, 0);
for (int i = 2; i >= 0; i--) {
for (int j = 2; j >= 0; j--) {
arr[i][j] = n % 10; n /= 10;
if (!arr[i][j]) {
ans.first = i;
ans.second = j;
}
}
}
return ans;
}
int getNum(vector<vector<int>>& arr) {
int ans = 0;
for (int i = 0; i <= 2; i++) {
for (int j = 0; j <= 2; j++) {
ans = ans * 10 + arr[i][j];
}
}
return ans;
}
int search(int start) {
int ans = 0;
vector<vector<int>> arr(3,vector<int>(3));
unordered_set<int> first,last;
first.insert(start);
last.insert(target);
queue<int> q,q2;
q.push(start);
q2.push(target);
while (!q.empty()) {
int len = q.size();
for (int i = 0; i < len; i++) {
int top = q.front(); q.pop();
if (last.count(top)) return ans;
pair<int, int> path = getZero(top, arr);
for (int j = 0; j < 4; j++) {
int nx = path.first + DIR[j][0];
int ny = path.second + DIR[j][1];
if (nx >= 0 && nx < 3 && ny >= 0 && ny < 3) {
swap(arr[path.first][path.second], arr[nx][ny]);
int num = getNum(arr);
if (!first.count(num)) {
first.insert(num);
q.push(num);
}
swap(arr[path.first][path.second], arr[nx][ny]);
}
}
}
ans++;
len = q2.size();
for (int i = 0; i < len; i++) {
int top = q2.front(); q2.pop();
if (first.count(top)) return ans;
pair<int, int> path = getZero(top, arr);
for (int j = 0; j < 4; j++) {
int nx = path.first + DIR[j][0];
int ny = path.second + DIR[j][1];
if (nx >= 0 && nx < 3 && ny >= 0 && ny < 3) {
swap(arr[path.first][path.second], arr[nx][ny]);
int num = getNum(arr);
if (!last.count(num)) {
last.insert(num);
q2.push(num);
}
swap(arr[path.first][path.second], arr[nx][ny]);
}
}
}
ans++;
}
return -1;
}
int main()
{
int start;
cin >> start;
cout << search(start) << endl;
return 0;
}