Buggy python submission (verdict: Runtime Error):
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input().strip()))
f=0 
for i in range(n):
    if f:
        break 
    for j in range(m):
        if mat[i][j]=='#':
            q=[[i,j]]
            f=1 
            vis=[[0 for x1 in range(m)]for y1 in range(n)]
            vis[i][j]=1 
            while q:
                t=q.pop(0)
                #print(t)
                x,y=t[0],t[1] 
                for k in range(4): 
                    if 0<=x+dx[k]<n and 0<=y+dy[k]<m and vis[x+dx[k]][y+dy[k]]==0 and mat[x+dx[k]][y+dy[k]]=='#': 
                        vis[x+dx[k]][y+dy[k]]=1 
                        q.append([x+dx[k],y+dy[k]])
            break 
for i in range(n):
    for j in range(m): 
        if vis[i][j]==0 and mat[i][j]=='#':
           # print(i,j)
            print('No')
            exit()
print('Yes')

Fixed submission:
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input().strip()))
f=0 
for i in range(n):
    for j in range(m):
        if mat[i][j]=='#':
            f=0 
            for k in range(4): 
                if 0<=i+dx[k]<n and 0<=j+dy[k]<m and mat[i+dx[k]][j+dy[k]]=='#': 
                    f=1  
            if not f:
                print('No')
                exit()
print('Yes')

Buggy python submission (verdict: Runtime Error):
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input().strip()))
f=0 
for i in range(n):
    if f:
        break 
    for j in range(m):
        if mat[i][j]=='#':
            q=[[i,j]]
            f=1 
            vis=[[0 for j in range(m)]for i in range(n)]
            vis[i][j]=1 
            while q:
                t=q.pop(0)
                #print(t)
                x,y=t[0],t[1] 
                for k in range(4): 
                    if 0<=x+dx[k]<n and 0<=y+dy[k]<m and vis[x+dx[k]][y+dy[k]]==0 and mat[x+dx[k]][y+dy[k]]=='#': 
                        vis[x+dx[k]][y+dy[k]]=1 
                        q.append([x+dx[k],y+dy[k]])
            break 
for i in range(n):
    for j in range(m): 
        if vis[i][j]==0 and mat[i][j]=='#':
           # print(i,j)
            print('No')
            exit()
print('Yes')

Fixed submission:
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input().strip()))
f=0 
for i in range(n):
    for j in range(m):
        if mat[i][j]=='#':
            f=0 
            for k in range(4): 
                if 0<=i+dx[k]<n and 0<=j+dy[k]<m and mat[i+dx[k]][j+dy[k]]=='#': 
                    f=1  
            if not f:
                print('No')
                exit()
print('Yes')

Buggy python submission (verdict: Runtime Error):
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input()))
f=0 
for i in range(n):
    if f:
        break 
    for j in range(m):
        if mat[i][j]=='#':
            q=[[i,j]]
            f=1 
            vis=[[0 for j in range(m)]for i in range(n)]
            vis[i][j]=1 
            while q:
                t=q.pop(0)
                #print(t)
                x,y=t[0],t[1] 
                for k in range(4): 
                    if 0<=x+dx[k]<n and 0<=y+dy[k]<m and vis[x+dx[k]][y+dy[k]]==0 and mat[x+dx[k]][y+dy[k]]=='#': 
                        vis[x+dx[k]][y+dy[k]]=1 
                        q.append([x+dx[k],y+dy[k]])
            break 
for i in range(n):
    for j in range(m): 
        if vis[i][j]==0 and mat[i][j]=='#':
           # print(i,j)
            print('No')
            exit()
print('Yes')

Fixed submission:
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input().strip()))
f=0 
for i in range(n):
    for j in range(m):
        if mat[i][j]=='#':
            f=0 
            for k in range(4): 
                if 0<=i+dx[k]<n and 0<=j+dy[k]<m and mat[i+dx[k]][j+dy[k]]=='#': 
                    f=1  
            if not f:
                print('No')
                exit()
print('Yes')

Buggy python submission (verdict: Runtime Error):
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input()))
f=0 
for i in range(n):
    if f:
        break 
    for j in range(m):
        if mat[i][j]=='#':
            q=[[i,j]]
            f=1 
            vis=[[0 for j in range(m)]for i in range(n)]
            vis[i][j]=1 
            while q:
                t=q.pop(0)
                #print(t)
                x,y=t[0],t[1] 
                for k in range(4): 
                    if 0<=x+dx[k]<n and 0<=y+dy[k]<m and vis[x+dx[k]][y+dy[k]]==0 and mat[x+dx[k]][y+dy[k]]=='#': 
                        vis[x+dx[k]][y+dy[k]]=1 
                        q.append([x+dx[k],y+dy[k]])
            break 
for i in range(n):
    for j in range(m): 
        if vis[i][j]==0 and mat[i][j]=='#':
           # print(i,j)
            print('No')
            exit()
print('Yes')

Fixed submission:
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input().strip()))
f=0 
for i in range(n):
    for j in range(m):
        if mat[i][j]=='#':
            f=0 
            for k in range(4): 
                if 0<=i+dx[k]<n and 0<=j+dy[k]<m and mat[i+dx[k]][j+dy[k]]=='#': 
                    f=1  
            if not f:
                print('No')
                exit()
print('Yes')

Buggy python submission (verdict: Runtime Error):
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input()))
f=0 
for i in range(n):
    if f:
        break 
    for j in range(n):
        if mat[i][j]=='#':
            q=[[i,j]]
            f=1 
            vis=[[0 for j in range(m)]for i in range(n)]
            vis[i][j]=1 
            while q:
                t=q.pop(0)
                x,y=t[0],t[1] 
                for k in range(4): 
                    if 0<=x+dx[k]<n and 0<=y+dy[k]<m and vis[x+dx[k]][y+dy[k]]==0: 
                        vis[x+dx[k]][y+dy[k]]=1 
                        q.append([x+dx[k],y+dy[k]])
            break 
for i in range(n):
    for j in range(m): 
        if vis[i][j]==0 and mat[i][j]=='#':
           # print(i,j)
            print('No')
            exit()
print('Yes')

Fixed submission:
n,m=map(int,input().split())
mat=[]
dx=[0,0,-1,1]
dy=[1,-1,0,0]
for i in range(n):
    mat.append(list(input().strip()))
f=0 
for i in range(n):
    for j in range(m):
        if mat[i][j]=='#':
            f=0 
            for k in range(4): 
                if 0<=i+dx[k]<n and 0<=j+dy[k]<m and mat[i+dx[k]][j+dy[k]]=='#': 
                    f=1  
            if not f:
                print('No')
                exit()
print('Yes')