Buggy python submission (verdict: Runtime Error):
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y] = 1: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if seen[x][y]==1:continue
          if S[x][y]=='@':break
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    if S[x0][y0]=='@':return 0
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if S[x][y]=='@':break
          if d[x][y] < d[x0][y0] + 1: break
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    if S[x0][y0]=='@':return 0
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if seen[x][y]==1:continue
          if S[x][y]=='@':break
          if d[x][y] < d[x0][y0] + 1: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
#from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[0 for i in range(W)] for j in range(H)]
    todo = []
    if S[x0][y0]=='@':return 0
    seen[x0][y0] = 1
    todo.append(x0*W+y0)
    for X in todo:
      x0,y0 = divmod(X,W)
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if seen[x][y]==1:continue
          if S[x][y]=='@':break
          seen[x][y] = 1
          todo.append(x*W+y)
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans > 0 else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[0 for i in range(W)] for j in range(H)]
    todo = deque()
    if S[x0][y0]=='@':return 0
    seen[x0][y0] = 1
    todo.append(x0*W+y0)
    while todo:
      x0,y0 = divmod(todo.popleft(),W)
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if seen[x][y]==1:continue
          if S[x][y]=='@':break
          seen[x][y] = 1
          todo.append(x*W+y)
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans > 0 else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[0 for i in range(W)] for j in range(H)]
    todo = deque()
    if S[x0][y0]=='@':return 0
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if seen[x][y]==1:continue
          if S[x][y]=='@':break
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans > 0 else -1)
  
if __name__ == "__main__":
  main()

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Runtime Error):
from collections import deque

H,W,K=map(int,input().split())
x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
S=[list(input()) for _ in range(H)]

def bfs(x0,y0,x_goal,y_goal):
  seen = [[0 for i in range(W)] for j in range(H)]
  d = [[0 for i in range(W)] for j in range(H)]
  todo = deque()
  if S[x0][y0]=='@':return 0
  seen[x0][y0] = 1
  todo.append((x0,y0))
  while todo:
    x0,y0 = todo.popleft()
    dx,dy = (1,-1,0,0),(0,0,1,-1)
    for i in range(4):
      for k in range(K):
        x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
        if x<0 or x>=H:break
        if y<0 or y>=W:break
        if seen[x][y]==1:continue
        if S[x][y]=='@':break
        seen[x][y] = 1
        todo.append((x,y))
        d[x][y] = d[x0][y0] + 1
        if x==x_goal and y == y_goal: return d[x][y]

ans = bfs(x1,y1,x2,y2)
print(ans if ans > 0 else -1)

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H,W,K=map(int,input().split())
x1,y1,x2,y2 = map(int,input().split())
start = (x1-1,y1-1);goal = (x2-1,y2-1)
S=[list(input()) for _ in range(H)]

def bfs(s):
  seen = [[0 for i in range(W)] for j in range(H)]
  d = [[0 for i in range(W)] for j in range(H)]
  todo = deque()
  now = s
  if S[now[0]][now[1]]=='@':return 0
  seen[now[0]][now[1]] = 1
  todo.append(now)
  while todo:
    now = todo.popleft()
    dx,dy = (1,-1,0,0),(0,0,1,-1)
    for i in range(4):
      for k in range(K):
        new = (now[0]+dx[i]*(k+1), now[1]+dy[i]*(k+1))
        if new[0]<0 or new[0]>=H:break
        if new[1]<0 or new[1]>=W:break
        if seen[new[0]][new[1]]==1:continue
        if S[new[0]][new[1]]=='@':break
        seen[new[0]][new[1]] = 1
        todo.append(new)
        d[new[0]][new[1]] = d[now[0]][now[1]] + 1
  return d

d = bfs(start)
print(d[goal[0]][goal[1]] if d[goal[0]][goal[1]] > 0 else -1)

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H,W,K=map(int,input().split())
x1,y1,x2,y2 = map(int,input().split())
start = (x1-1,y1-1);goal = (x2-1,y2-1)
S=[input() for _ in range(H)]

def bfs(s):
  seen = [[0 for i in range(W)] for j in range(H)]
  d = [[0 for i in range(W)] for j in range(H)]
  todo = deque()
  now = s
  if S[now[0]][now[1]]=='@':return 0
  seen[now[0]][now[1]] = 1
  todo.append(now)
  while todo:
    now = todo.popleft()
    dx,dy = (1,-1,0,0),(0,0,1,-1)
    for i in range(4):
      for k in range(K):
        new = (now[0]+dx[i]*(k+1), now[1]+dy[i]*(k+1))
        if new[0]<0 or new[0]>=H:break
        if new[1]<0 or new[1]>=W:break
        if seen[new[0]][new[1]]==1:continue
        if S[new[0]][new[1]]=='@':break
        seen[new[0]][new[1]] = 1
        todo.append(new)
        d[new[0]][new[1]] = d[now[0]][now[1]] + 1
  return d

d = bfs(start)
print(d[goal[0]][goal[1]] if d[goal[0]][goal[1]] > 0 else -1)

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H,W,K=map(int,input().split())
x1,y1,x2,y2 = map(int,input().split())
start = (x1-1,y1-1);goal = (x2-1,y2-1)
S=[input() for _ in range(H)]

def bfs(s):
  seen = [[0 for i in range(W)] for j in range(H)]
  d = [[0 for i in range(W)] for j in range(H)]
  todo = deque()
  now = s
  if S[now[0]][now[1]]=='@':return 0
  seen[now[0]][now[1]] = 1
  todo.append(now)
  while 1:
    if len(todo)==0:break
    now = todo.popleft()
    dx,dy = (1,-1,0,0),(0,0,1,-1)
    for i in range(4):
      for k in range(K):
        new = (now[0]+dx[i]*(k+1), now[1]+dy[i]*(k+1))
        if new[0]<0 or new[0]>=H:break
        if new[1]<0 or new[1]>=W:break
        if seen[new[0]][new[1]]==1:continue
        if S[new[0]][new[1]]=='@':break
        seen[new[0]][new[1]] = 1
        todo.append(new)
        d[new[0]][new[1]] = d[now[0]][now[1]] + 1
  return d

d = bfs(start)
print(d[goal[0]][goal[1]] if d[goal[0]][goal[1]] > 0 else -1)

Fixed submission:
from collections import deque

def main():
  H,W,K=map(int,input().split())
  x1,y1,x2,y2 = map(lambda x: int(x)-1,input().split())
  S=[list(input()) for _ in range(H)]
  INF = 10**20

  def bfs(x0,y0,x_goal,y_goal):
    seen = [[0 for i in range(W)] for j in range(H)]
    d = [[INF for i in range(W)] for j in range(H)]
    d[x0][y0] = 0
    todo = deque()
    seen[x0][y0] = 1
    todo.append((x0,y0))
    while todo:
      x0,y0 = todo.popleft()
      dx,dy = (1,-1,0,0),(0,0,1,-1)
      for i in range(4):
        for k in range(K):
          x,y = x0+dx[i]*(k+1), y0+dy[i]*(k+1)
          if x<0 or x>=H:break
          if y<0 or y>=W:break
          if d[x][y] < d[x0][y0] + 1: break
          if S[x][y]=='@':break
          if seen[x][y]: continue
          seen[x][y] = 1
          todo.append((x,y))
          d[x][y] = d[x0][y0] + 1
          if x==x_goal and y == y_goal: return d[x][y]
    return d[x_goal][y_goal]

  ans = bfs(x1,y1,x2,y2)
  print(ans if ans < INF else -1)
  
if __name__ == "__main__":
  main()