dfs+bfs專題（簡單題）

A.迷宮問題 POJ 3984

bfs + 輸出路徑

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;
int maze[5][5];
int way[4][2] = {0,1,1,0,-1,0,0,-1};
struct node
{
    int x,y,s,pre;
    node(int a,int b,int c,int d)
    {x = a; y = b; s = c; pre = d;}
    node(){}
}ans[110];
int sta[105];
void bfs()
{
    queue<node> q;
    q.push(node(0,0,0,-1));
    int num = 0;
    while(!q.empty())
    {
        node temp = q.front();  q.pop();
        ans[num++] = temp;
        int x = temp.x,y = temp.y;
        if(x == 4 && y == 4)    break;
        for(int i = 0; i < 4; i++)
        {
            int newx = x + way[i][0] , newy = y + way[i][1];
            if(maze[newx][newy] || newx < 0 || newx > 4 || newy < 0 || newy > 4) continue;
            maze[newx][newy] = 1;
            node no = node(newx,newy,temp.s+1,num-1);
            q.push(no);
        }
    }
    int th = num - 1, snum = 0;
    while(ans[th].pre != -1)
    {
        sta[++snum] = ans[th].pre;
        th = ans[th].pre;
    }
    while(snum != 0)
    {
        printf("(%d, %d)\n",ans[sta[snum]].x,ans[sta[snum]].y);
        snum--;
    }
    printf("(4, 4)\n");
}
int main()
{
    for(int i = 0; i < 5; i++)
    for(int j = 0; j < 5; j++)
        scanf("%d",&maze[i][j]);
    bfs();
    return 0;
}

B.棋盤問題 POJ 1321

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;
int col[10];
int maze[10][10];
int n,m;
char s[15];
int ans = 0;
void dfs(int nowr,int num)
{
    if(num == m) {  ans++ ; return;}
    if(nowr >= n) return;
    for(int i = 0; i < n; i++)
    {
        if(maze[nowr][i] || col[i]) continue;
        col[i] = 1;
        dfs(nowr+1,num+1);
        col[i] = 0;
    }
    dfs(nowr + 1, num);
}
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        if(n == -1 && m == -1) break;
        for(int i = 0; i < n; i++)
        {
            scanf("%s",s);
            for(int j = 0; j < n ; j++)
                maze[i][j] = s[j] == '#'?0:1;
        }
        ans = 0;
        dfs(0,0);
        printf("%d\n",ans);
    }
    return 0;
}

C.三維迷宮問題 POJ 2251

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std;
const int maxn = 35;
struct node
{
    int x,y,z,s;
    node(int a,int b,int c,int d){x = a; y = b; z = c; s = d;}
};
int maze[maxn][maxn][maxn];
int way[6][3] = {0,0,1,0,0,-1,0,1,0,0,-1,0,1,0,0,-1,0,0};
int st[3],p[3];
char s[100];
int m,n,Q;
void bfs()
{
    queue<node > q;
    q.push(node(st[0],st[1],st[2],0));
    int flag = 0;
    maze[st[0]][st[1]][st[2]] = 1;
    while(!q.empty())
    {
        node temp = q.front(); q.pop();
        int x = temp.x, y = temp.y, z = temp.z, s = temp.s;
        if(x == p[0] && y == p[1] && z == p[2])
        {
            flag = 1;
            printf("Escaped in %d minute(s).\n",s);
            break;
        }
        for(int i = 0; i < 6; i++)
        {
            int nx = x + way[i][0], ny = y + way[i][1] , nz = z + way[i][2];
            if(maze[nx][ny][nz] || nx < 0 || nx >= m || ny < 0 || ny >= n || nz < 0 || nz >= Q) continue;
            maze[nx][ny][nz] = 1;
            q.push(node(nx,ny,nz,s+1));
        }
    }
    if(!flag)   printf("Trapped!\n");
}
int main()
{
    while(~scanf("%d%d%d",&m,&n,&Q) && n+m+Q)
    {
        for(int i = 0; i < m; i++)
        for(int j = 0; j < n; j++)
        {
            scanf("%s",s);
            for(int k = 0; k < Q;k ++)
            {
                maze[i][j][k] = 0;
                if(s[k] == 'S') st[0] = i,st[1] = j,st[2] = k;
                else if(s[k] == 'E') p[0] = i,p[1] = j,p[2] = k;
                else if(s[k] == '#') maze[i][j][k] = 1;
            }
        }
        bfs();
    }

    return 0;
}

D.一個追牛的人的問題，記得空間別開小，會gg POJ 3278

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;
const int maxn = 1e5 + 10;
int n,k;
struct node
{
    int v,s;
    node(int a,int b){v = a; s = b;}
};
int vis[maxn*2];
int bfs()
{
    queue<node> q;
    q.push(node(n,0));
    for(int i = 0; i < maxn; i++)   vis[i] = 0;
    vis[n] = 1;
    while(!q.empty())
    {
        node temp = q.front(); q.pop();
        if(temp.v == k)
        {
            printf("%d\n",temp.s);
            break;
        }
        int nx = temp.v + 1,ns = temp.s + 1;
        if(nx <= k + 1 && !vis[nx]) {vis[nx] = 1;q.push(node(nx,ns));}
        nx = temp.v * 2;
        if(nx < 2*k && !vis[nx]) {vis[nx] = 1;q.push(node(nx,ns));}
        nx = temp.v-1;
        if(nx >= 0 && !vis[nx]) {vis[nx] = 1;q.push(node(nx,ns));}
    }
}
int main()
{
    while(~scanf("%d%d",&n,&k))
        bfs();
    return 0;
}

E.這個應該叫開關問題 POJ 3279

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;
int ori[20][20];
int op[20][20];
int moni[20][20];
int way[4][2] = {0,1,0,-1,1,0,-1,0};
int n,m;
bool ans = false;
void filp(int i,int j)
{
    moni[i][j] = !moni[i][j];
    for(int x = 0; x < 4; x++)
    {
        int nx = i + way[x][0] , ny = j + way[x][1];
        if(nx < 0 || nx >= n || ny < 0 || ny >= m) continue;
        moni[nx][ny] = !moni[nx][ny];
    }
}
void conti(int time)
{
    for(int i = 1; i < n; i++)
    for(int j = 0; j < m; j++)
    {
        if(moni[i-1][j])
            {op[i][j] = 1;filp(i,j);}
    }
    int flag = 1;
    for(int i = 0; i < m; i++)
        if(moni[n-1][i]) { flag = 0; break;}
    if(flag)
    {
        ans = true;
        for(int i = 0; i < n ; i++)
        {
            for(int j = 0; j < m ; j++)
                j == 0?printf("%d",op[i][j]) : printf(" %d",op[i][j]);
            printf("\n");
        }
    }
}
void solve()
{
    ans = false;
    for(int i = 0; i < (1 << m); i++)   //翻轉第一行的全部情況
    {
        if(ans) break;
        memset(op,0,sizeof(op));
        memcpy(moni,ori,sizeof(ori));
        int x = 0;
        for(int j = 1; j <= i; j = (1<<x))
        {
            if((j&i) == j) {op[0][x] = 1, filp(0,x);}
            x++;
        }
        conti(i);
    }

    if(ans == false) printf("IMPOSSIBLE\n");
}

int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        for(int i = 0; i < n ; i++)
        for(int j = 0; j < m ; j++)
            scanf("%d",&ori[i][j]);
        solve();
    }
    return 0;
}

F.一個非要素數的問題  POJ 3126

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>
#include <cmath>
using namespace std;
int a,b;
struct node
{
    int to,s;
    int val[4];
    node(){}
    node(int a,int b)
    {
        to = a; s = b;
        val[0] = to/1000, val[1] = to/100%10,
        val[2] = to/10%10, val[3] = to%10;
    }
};
int prime[10000];
int vis[10000];
bool isPrime(int n)
{
   // cout << n <<endl;
   int temp = (int)sqrt(n*1.0);
    for(int i = 2; i <= temp ; i++)
        if(n%i == 0) return 0;
    return 1;
}

void pre()
{
    for(int i = 1000; i < 10000; i++)
        if(isPrime(i))   prime[i] = 1;
}

int bfs()
{
    memset(vis,0,sizeof(vis));
    queue<node> q;
    q.push(node(a,0));
    vis[a] = 1;
    while(!q.empty())
    {
        node temp = q.front(); q.pop();
        int to = temp.to, s = temp.s;
        if(to == b) {printf("%d\n",s); break;}
        int nval[4];
        for(int i = 0; i < 4; i++) nval[i] = temp.val[i];

        for(int i = 0; i < 4; i++)
        for(int j = 0; j < 10; j++)
        {
            int newval = 0;
            for(int k = 0; k < 4; k++)
                if(k != i)  newval = (newval * 10) + nval[k];
                else newval = (newval*10) + j;
            if(!vis[newval] && prime[newval])
                vis[newval] = 1, q.push(node(newval,s+1));
        }
    }
}
int main()
{
    pre();
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d",&a,&b);
        bfs();
    }
    return 0;
}

G.HDU 1010

一個我已經寫過還是超時的問題

記得需要奇偶剪枝。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <cmath>
using namespace std;
const int inf = 0x3f3f3f3f;
const int maxn = 10;
int maze[maxn][maxn];
bool vis[maxn][maxn];
int way[4][2] = {1,0,-1,0,0,-1,0,1};
int s[2],p[2];
int n,m,t;
bool ans = false;
int dis(int x,int y)
{
    int thdis = abs(x-p[0]) + abs(y-p[1]);
    return thdis;
}

int dfs(int x,int y,int step)
{
    if(x == p[0] && y == p[1] && step == t){ans = true; return 1;}
    if(ans) return 1;
    if(step + dis(x,y) > t) return 0;
    for(int i = 0; i < 4; i++)
    {
        int newx = x + way[i][0] , newy = y + way[i][1];
        if(!vis[newx][newy] && newx >= 0 && newx < n &&
           newy >= 0 && newy < m && maze[newx][newy] == 0
           && step + 1 <= t)
        {
            int mdis = dis(newx,newy);
            if(((t - (step+1) - mdis)%2)) return 0;

            vis[newx][newy] = 1;
            if(dfs(newx,newy,step+1)) return 1;
            vis[newx][newy] = 0;
        }
    }
    return 0;
}
char str[1000];
int main()
{
    while(~scanf("%d%d%d",&n,&m,&t) && n+m+t)
    {
        ans = 0;
        memset(vis,0,sizeof(vis));
        for(int i = 0 ; i < n ; i++)
        {
            scanf("%s",str);
            for(int j = 0 ; j < m ; j++)
            {
                maze[i][j] = 0;
                if(str[j] == 'S') s[0] = i, s[1] = j;
                else if(str[j] == 'D') p[0] = i, p[1] = j;
                else if(str[j] == 'X') maze[i][j] = 1;
            }
        }
        vis[s[0]][s[1]] = 1;
        dfs(s[0],s[1],0);
        vis[s[0]][s[1]] = 0;
        int sdis = dis(s[0],s[1]);
        if((t - sdis) % 2 != 0 || t < sdis) {printf("NO\n"); continue;}
        ans == 1 ? printf("YES\n") : printf("NO\n");
    }
    return 0;
}

H.比油田更簡單的flood  fill HDU 1312

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;
int maze[30][30];

char str[1000];
int st[2];
int way[4][2] = {0,1,0,-1,-1,0,1,0};
int ans = 0,n,m;
void dfs(int x,int y)
{
    ans ++;
    for(int i = 0; i < 4; i++)
    {
        int nx = x + way[i][0], ny = y + way[i][1];
        if(!maze[nx][ny] && nx >= 0 && ny >= 0
           && nx  < n && ny < m)
        {
            maze[nx][ny] = 1;
            dfs(nx,ny);
        }
    }
}
int main()
{
    while(~scanf("%d%d",&m,&n) && n+m)
    {
        ans = 0;
        for(int i = 0; i < n; i++)
        {
            scanf("%s",str);
            for(int j = 0; j < m; j++)
            {
                maze[i][j] = 0;
                if(str[j] == '#') maze[i][j] = 1;
                if(str[j] == '@') st[0] = i,st[1] = j;
            }
        }
        maze[st[0]][st[1]] = 1;
        dfs(st[0],st[1]);
        printf("%d\n",ans);
    }
    return 0;
}

I.油田問題

比上面那個稍稍難一點的flood fill HDU 1241

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;
int maze[150][150];

char str[1000];
int st[2];
int way[8][2] = {0,1,0,-1,-1,0,1,0,1,1,1,-1,-1,1,-1,-1};
int ans,n,m;
void dfs(int x,int y)
{
    for(int i = 0; i < 8; i++)
    {
        int nx = x + way[i][0], ny = y + way[i][1];
        if(!maze[nx][ny] && nx >= 0 && ny >= 0
           && nx  < n && ny < m)
        {
            maze[nx][ny] = 1;
            dfs(nx,ny);
        }
    }
}
int main()
{
    while(~scanf("%d%d",&n,&m) && n+m)
    {
        ans = 0;
        for(int i = 0; i < n; i++)
        {
            scanf("%s",str);
            for(int j = 0; j < m; j++)
            {
                maze[i][j] = 0;
                if(str[j] == '*') maze[i][j] = 1;
            }
        }
        for(int i = 0; i < n ; i++)
        for(int j = 0; j < m ; j++)
        {
            if(maze[i][j] == 0)
            {
                ans ++;
                maze[i][j] = 1;
                dfs(i,j);
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}

J.論如何逃出火災現場問題 UVA 11624

什麼，一個bfs不行？那就兩個好了

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
const int maxn = 1050;
const int inf = 0x3f3f3f3f;
char str[maxn];
int Time[maxn][maxn];
int maze[maxn][maxn];
int vis[maxn][maxn];
int f[maxn][2],J[2];
int way[4][2] = {1,0,-1,0,0,1,0,-1};

int fnum = 0,n,m;
struct node
{
    int x,y,t;
    node(int a,int b,int c){x = a ; y = b ; t = c ;}
};
void bfspre()
{
    memset(vis,0,sizeof(vis));
    memset(Time,inf,sizeof(Time));
    queue<node> q;
    for(int i = 0; i < fnum; i++)
    {
        vis[ f[i][0] ][f [i][1] ] = Time[f[i][0]][f[i][1]] = 1;
        q.push(node(f[i][0],f[i][1],0));
    }
    while(!q.empty())
    {
        node temp = q.front(); q.pop();
        int x = temp.x, y = temp.y, t = temp.t;
        Time[x][y] = t;
        for(int i = 0; i < 4; i++)
        {
            int nx = x + way[i][0] , ny = y + way[i][1];
            if(nx < 0 || nx >= n || ny < 0 || ny >= m || maze[nx][ny]) continue;
            if(!vis[nx][ny])
            {
                vis[nx][ny] = 1;
                q.push(node(nx,ny,t+1));
            }
        }
    }
}
void bfs()
{
    queue<node>q;
    q.push(node(J[0],J[1],0));
    maze[J[0]][J[1]] = 1;
    int mark = 0;
    while(!q.empty())
    {
        node temp = q.front(); q.pop();
        int x = temp.x, y = temp.y, t = temp.t;
        for(int i = 0; i < 4; i++)
        {
            int nx = x + way[i][0] , ny = y + way[i][1];
            if(nx < 0 || ny < 0 || nx >= n || ny >= m)
            {
                printf("%d\n",t + 1);
                mark = 1;
                break;
            }
            if(maze[nx][ny]) continue;
            if(!maze[nx][ny] && t + 1 < Time[nx][ny])
            {
                maze[nx][ny] = 1;
                q.push(node(nx , ny , t+1));
            }
        }
        if(mark) break;
    }
    if(!mark) printf("IMPOSSIBLE\n");
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        fnum = 0;
        scanf("%d%d",&n,&m);
        for(int i = 0; i < n; i++)
        {
            scanf("%s",str);
            for(int j = 0; j < n; j++)
            {
                maze[i][j] = 0;
                if(str[j] == '#') maze[i][j] = 1;
                if(str[j] == 'F') f[fnum][0] = i, f[fnum++][1] = j;
                if(str[j] == 'J') J[0] = i, J[1] = j;
            }
        }
        bfspre();
        bfs();
    }
    return 0;
}

K.閒着無聊倒水玩兒問題 POJ 3414

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <iostream>
#include <queue>
using namespace std;
struct node
{
    int i,j,s,way,pre;
    node(){}
    node(int a,int b,int c,int d){i = a; j = b; s = c;pre = d;}
}pro[1005];
bool vis[105][105];
int anum = 1;
int a,b,c;
char out[10][20] = {" ","FILL(1)", "FILL(2)", "DROP(1)" , "DROP(2)", "POUR(1,2)", "POUR(2,1)"};
void print(int id)
{
    if(pro[id].pre != 1)
        print(pro[id].pre);
    printf("%s\n",out[pro[id].way]);
}

void bfs()
{
    int mark = 0;
    anum = 1;
    memset(vis,0,sizeof(vis));
    queue<node > q;
    q.push(node(0,0,0,0));
    while(!q.empty())
    {
        node temp = q.front(); q.pop();
        pro[anum++] = temp;
        int x = temp.i, y = temp.j, s = temp.s;
        //cout << x <<" " << y << endl;
        if(x == c || y == c)
        {
            printf("%d\n",s);
            print(anum-1);
            mark = 1;
            break;
        }
        node change = node(a,y,s+1,anum-1);
        if(!vis[a][y])
            change.way = 1, vis[a][y] = 1,q.push(change);
        change.i = x, change.j = b;
        if(!vis[x][b])
            change.way = 2,vis[x][b] = 1,q.push(change);
        change.i = 0, change.j = y;
        if(!vis[0][y])
            change.way = 3,vis[0][y] = 1,q.push(change);
        if(!vis[x][0])
            change.way = 4, vis[x][0] = 1,change.i = x, change.j = 0,q.push(change);

        if(y+x > b)
        {
            change.i = y+x-b, change.j = b;
            if(!vis[y+x-b][b])
                vis[y+x-b][b] = 1, change.way = 5, q.push(change);
        }
        else
        {
            change.i = 0, change.j = y+x;
            if(!vis[0][y+x])
                vis[0][y+x] = 1, change.way = 5, q.push(change);
        }
        if(x+y > a)
        {
            change.i = a, change.j = x+y-a;
            if(!vis[a][x+y-a])
                vis[a][x+y-a] = 1, change.way = 6, q.push(change);
        }
        else
        {
            change.i = x+y, change.j = 0;
            if(!vis[x+y][0])
                vis[x+y][0] = 1,change.way = 6,q.push(change);
        }
    }
    if(!mark) printf("impossible\n");
}

int main()
{
    while(~scanf("%d%d%d",&a,&b,&c))
    {
        bfs();
    }
    return 0;
}

L.並不是bfs + dfs 只是模擬題 POJ 3087

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;
char s1[150],s2[150];
char temp1[150], temp2[150];
char sta[300],tar[300];


int main()
{
    int t,n;
    scanf("%d",&t);
    for(int kase = 1; kase <= t; kase ++)
    {
        scanf("%d",&n);
        scanf("%s%s%s",s1,s2,tar);
        int num = 0;
        while(num < 10000)
        {
            for(int i = 0; i < 2*n; i++)  sta[i] = i%2?s1[i/2] : s2[i/2];
            sta[2*n] = '\0';
            num++;
            if(strcmp(sta,tar) == 0) break;
            for(int i = 0; i < n; i++)
                s1[i] = sta[i]; s1[n] = '\0';
            for(int i = n; i <= 2*n; i++)
                s2[i-n] = sta[i]; s2[2*n] = '\0';
           // cout << sta << " " << s1 << " " << s2 << endl;
        }
        printf("%d ",kase);
        if(num == 10000)    printf("-1\n");
        else printf("%d\n",num);
    }
    return 0;
}