Acwing improvement–multi-source BFS+minimum step model+double-ended queue wide search

Multi-source BFS

1. Matrix distance

Titlehttps://www.acwing.com/problem/content/description/175/

#include <bits/stdc++.h>
using namespace std;
#define x first
#define y second
typedef pair<int,int> PII;
const int N=1010;
char g[N][N];
int dist[N][N];
PII q[N*N];
int n,m;
int dx[]={-1,0,1,0},dy[]={0,-1,0,1};
void bfs()
{
    memset(dist,-1, sizeof dist);
    int hh=0,tt=-1;
    for(int i=0;i<n;i++)
        for(int j=0;j<m;j++)
            if(g[i][j]=='1')
            {
                dist[i][j]=0;
                q[ + + tt]={i,j};
            }
    while(hh<=tt)
    {
        auto t=q[hh++];
        for(int i=0;i<4;i++)
        {
            int xx=t.x + dx[i],yy=t.y + dy[i];
            if(xx<0||xx>=n||yy<0||yy>=m)continue;
            if(dist[xx][yy]!=-1)continue;
            dist[xx][yy]=dist[t.x][t.y] + 1;
            q[ + + tt]={xx,yy};
        }
    }
}
int main()
{
    cin>>n>>m;
    for(int i=0;i<n;i ++ )scanf("%s",g[i]);
    bfs();
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<m;j++)
            cout<<dist[i][j]<<" ";
        cout<<endl;
    }
}

Minimum step model

Magic Board

Titlehttps://www.acwing.com/problem/content/description/1109/

#include <bits/stdc++.h>
using namespace std;
char g[2][8];
unordered_map<string,int> dist;
unordered_map<string,pair<char,string>> pre;
queue<string> q;
void Set(string str)
{
    for(int i=0;i<4;i ++ )g[0][i]=str[i];
    for(int i=3,j=4;i>=0;i--,j + + )g[1][i]=str[j];
}
string get()
{
    string res;
    for(int i=0;i<4;i + + )res + =g[0][i];
    for(int i=3;i>=0;i--)res + =g[1][i];
    return res;
}
string move0(string state)
{
    Set(state);
    for(int i=0;i<4;i++)
    swap(g[0][i],g[1][i]);
    return get();
}
string move1(string state)
{
    Set(state);
    char v0=g[0][3],v1=g[1][3];
    for(int i=3;i>0;i--)
    for(int j=0;j<2;j++)
    g[j][i]=g[j][i-1];
    g[0][0]=v0,g[1][0]=v1;
    return get();
}
string move2(string state)
{
    Set(state);
    char v=g[0][1];
    g[0][1]=g[1][1];
    g[1][1]=g[1][2];
    g[1][2]=g[0][2];
    g[0][2]=v;
    return get();
}
void bfs(string start, string end)
{
    if(start==end) return;
    q. push(start);
    dist[start]=0;
    while(q. size())
    {
        auto t=q. front();
        q. pop();
        
        string m[3];
        m[0]=move0(t);
        m[1]=move1(t);
        m[2]=move2(t);
        
        for(int i=0;i<3;i++)
        {
            string str=m[i];
            if(dist.count(str)==0)
            {
                dist[str]=dist[t] + 1;
                pre[str]={char(i + 'A'),t};
                if(str==end)break;
                q. push(str);
            }
        }
    }
}
int main()
{
    string start, end;
    for(int i=0;i<8;i ++ )
    {
        int x;
        cin>>x;
        end + =char(x + '0');
    }
    for(int i=0;i<8;i + + )start + =char(i + '1');
    
    bfs(start,end);
    
    cout<<dist[end]<<endl;
    
    string res;
    while(end!=start)
    {
        res + =pre[end].first;
        end=pre[end].second;
    }
    reverse(res.begin(),res.end());
    if(res. size())
    cout<<res;
}

Double-ended queue wide search (when the weight is only 0 and 1)

circuit repair

Titlehttps://www.acwing.com/problem/content/description/177/

Solutionhttps://www.acwing.com/solution/content/21775/

#include <bits/stdc++.h>
using namespace std;
#define x first
#define y second
typedef pair<int,int> PII;
const int N=550;

char g[N][N];
int dist[N][N];
bool st[N][N];

int n,m;
char cs[5]="\/\/";//Four standard directions\/\/, used to compare whether the directions on the map are consistent
int dx[]={-1,-1,1,1},dy[]={-1,1,1,-1};//direction of conversion, \/\/
int ix[]={-1,-1,0,0},iy[]={-1,0,0,-1};//corresponding to the coordinates of the map\/\/


int bfs()
{
    deque<PII> q;//double-ended queue
    memset(st,0,sizeof st);//clear state
    memset(dist,0x3f,sizeof dist);//clear the distance
    
    q.push_back({0,0});
    dist[0][0]=0;
    
    while(q. size())
    {
        auto t=q. front();
        q. pop_front();
        
        int x=t.x,y=t.y;
        if(x==n & amp; & amp;y==m) return dist[x][y];//If n and m have been found, return directly
        
        if(st[x][y])continue;
        st[x][y]=true;
        
        for(int i=0;i<4;i++)
        {
            int a = x + dx[i],b = y + dy[i];
            if(a<0||a>n||b<0||b>m)continue;
            int ga=x + ix[i],gb=y + iy[i];
            int w=(g[ga][gb]!=cs[i]);//Check if the original image is in the same direction as my transfer, if it is 0, anyway it is 1
            int d = dist[x][y] + w;
            if(d<dist[a][b])//If the distance is less than the distance to me
            {
                dist[a][b]=d;//Then update the minimum distance
                if(!w)q.push_front({a,b});//If it is 0, put the front of the queue
                else q.push_back({a,b});//If it is 1, put it at the end of the queue
            }
        }
    }
    return -1;//will not be executed
}
int main()
{
    int t;
    cin>>t;
    while(t--)
    {
        cin>>n>>m;
        
        for(int i=0;i<n;i++)
        for(int j=0;j<m;j++)
        cin>>g[i][j];
        
        if( n + m & amp; 1) cout<<"NO SOLUTION"<<endl;//Analysis is available, if the sum is unreachable at odd points
        else cout<<bfs()<<endl;
    }
    
}