Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
sx,sy,tx,ty = map(int,input().split())
ans_list = []
(tx,ty) = (tx-sx,ty-sy); (sx,sy) = (0,0)
H,W = ty+3,tx+3
visited = [[0]*(tx+3) for i in range(ty+3)]
d = [[1,0],[0,1],[-1,0],[0,-1]]
(sx,sy) = (sx+1,sy+1); (tx,ty) = (tx+1,ty+1)
def bfs(si,sj,gi,gj):
    tr = [[si,sj]]
    q = deque([[si,sj,tr]])
    while q:
        i,j,tr = q.popleft()
        if (i,j) == (gi,gj):
            return tr
        for di,dj in d:
            ni = i + di; nj = j + dj
            if 0 <= ni <= H-1 and 0 <= nj <= W-1 and visited[ni][nj] == 0:
                visited[ni][nj] = 1
                ntr = tr[:]; ntr.append([ni,nj])
                q.append([ni,nj,ntr])

def change(tr):
    def func(d):
        if d == (1,0):return "U"
        if d == (-1,0):return "D"
        if d == (0,-1):return "L"
        if d == (0,1):return "R"
    for i in range(len(tr)-1):
        (ni,nj) = (tr[i+1][0],tr[i+1][1])
        (i,j) = (tr[i][0],tr[i][1])
        d = (ni-i,nj-j)
        ans_list.append(func(d))

tr = []
for cnt in range(2):
    res = bfs(sy,sx,ty,tx)
    for k in range(1,len(res)):
        i,j = res[k][0],res[k][1]
        rei, rej = ty + sx - i, tx + sy - j
        res.append([rei,rej])
    if cnt == 0:
        tr += res
    else:
        tr += res[1:]
    visited = [[0]*W for i in range(H)]
    for i,j in tr:
        visited[i][j] = 1
    visited[ty][tx] = 0

change(tr)
ans = "".join(ans_list)
print(ans)

Fixed submission:
sx,sy,tx,ty = map(int,input().split())
(tx,ty) = (tx-sx,ty-sy)
route1 = "U"*ty + "R"*tx
route2 = "D"*ty + "L"*tx
route3 = "L" + "U"*(ty+1) + "R"*(tx+1) + "D"
route4 = "R" + "D"*(ty+1) + "L"*(tx+1) + "U"
ans = route1 + route2 + route3 + route4
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
sx,sy,tx,ty = map(int,input().split())
ans_list = []
(tx,ty) = (tx-sx,ty-sy); (sx,sy) = (0,0)
H,W = ty+3,tx+3
visited = [[0]*(tx+3) for i in range(ty+3)]
d = [[1,0],[0,1],[-1,0],[0,-1]]
(sx,sy) = (sx+1,sy+1); (tx,ty) = (tx+1,ty+1)
def bfs(si,sj,gi,gj):
    tr = [[si,sj]]
    q = deque([[si,sj,tr]])
    while q:
        i,j,tr = q.popleft()
        if (i,j) == (gi,gj):
            return tr
        for di,dj in d:
            ni = i + di; nj = j + dj
            if 0 <= ni <= H-1 and 0 <= nj <= W-1 and visited[ni][nj] == 0:
                visited[ni][nj] = 1
                ntr = tr[:]; ntr.append([ni,nj])
                q.append([ni,nj,ntr])

def change(tr):
    def func(d):
        if d == (1,0):return "U"
        if d == (-1,0):return "D"
        if d == (0,-1):return "L"
        if d == (0,1):return "R"
    for i in range(len(tr)-1):
        (ni,nj) = (tr[i+1][0],tr[i+1][1])
        (i,j) = (tr[i][0],tr[i][1])
        d = (ni-i,nj-j)
        ans_list.append(func(d))

tr = []
for cnt in range(2):
    res = bfs(sy,sx,ty,tx)
    for k in range(1,len(res)):
        i,j = res[k][0],res[k][1]
        rei, rej = ty + sx - i, tx + sy - j
        res.append([rei,rej])
    if cnt == 0:
        tr += res
    else:
        tr += res[1:]
    visited = [[0]*W for i in range(H)]
    for i,j in tr:
        visited[i][j] = 1
    visited[ty][tx] = 0

change(tr)
ans = "".join(ans_list)
print(ans)

Fixed submission:
sx,sy,tx,ty = map(int,input().split())
(tx,ty) = (tx-sx,ty-sy)
route1 = "U"*ty + "R"*tx
route2 = "D"*ty + "L"*tx
route3 = "L" + "U"*(ty+1) + "R"*(tx+1) + "D"
route4 = "R" + "D"*(ty+1) + "L"*(tx+1) + "U"
ans = route1 + route2 + route3 + route4
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
sx,sy,tx,ty = map(int,input().split())
ans_list = []
(tx,ty) = (tx-sx,ty-sy); (sx,sy) = (0,0)
H,W = ty+3,tx+3
visited = [[0]*(tx+3) for i in range(ty+3)]
d = [[1,0],[0,1],[-1,0],[0,-1]]
(sx,sy) = (sx+1,sy+1); (tx,ty) = (tx+1,ty+1)
def bfs(si,sj,gi,gj):
    tr = [[si,sj]]
    q = deque([[si,sj,tr]])
    while q:
        i,j,tr = q.popleft()
        if (i,j) == (gi,gj):
            return tr
        for di,dj in d:
            ni = i + di; nj = j + dj
            if 0 <= ni <= H-1 and 0 <= nj <= W-1 and visited[ni][nj] == 0:
                visited[ni][nj] = 1
                ntr = tr[:]; ntr.append([ni,nj])
                q.append([ni,nj,ntr])

def change(tr):
    def func(d):
        if d == (1,0):return "U"
        if d == (-1,0):return "D"
        if d == (0,-1):return "L"
        if d == (0,1):return "R"
    for i in range(len(tr)-1):
        (ni,nj) = (tr[i+1][0],tr[i+1][1])
        (i,j) = (tr[i][0],tr[i][1])
        d = (ni-i,nj-j)
        ans_list.append(func(d))

res = []
for i in range(4):
    if i == 0:
        res += bfs(sy,sx,ty,tx)
    else:
        res = res[:-1] + bfs(sy,sx,ty,tx)
    visited = [[0]*W for i in range(H)]
    for i,j in res:
        visited[i][j] = 1
    sy,ty = ty,sy; sx,tx = tx,sx
    visited[ty][tx] = 0

change(res)
ans = "".join(ans_list)
print(ans)

Fixed submission:
sx,sy,tx,ty = map(int,input().split())
(tx,ty) = (tx-sx,ty-sy)
route1 = "U"*ty + "R"*tx
route2 = "D"*ty + "L"*tx
route3 = "L" + "U"*(ty+1) + "R"*(tx+1) + "D"
route4 = "R" + "D"*(ty+1) + "L"*(tx+1) + "U"
ans = route1 + route2 + route3 + route4
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
sx,sy,tx,ty = map(int,input().split())
ans_list = []
(tx,ty) = (tx-sx,ty-sy); (sx,sy) = (0,0)
H,W = ty+3,tx+3
visited = [[0]*(tx+3) for i in range(ty+3)]
d = [[1,0],[0,1],[-1,0],[0,-1]]
(sx,sy) = (sx+1,sy+1); (tx,ty) = (tx+1,ty+1)
def bfs(si,sj,gi,gj):
    tr = [[si,sj]]
    q = deque([[si,sj,tr]])
    while q:
        i,j,tr = q.popleft()
        if (i,j) == (gi,gj):
            return tr
        for di,dj in d:
            ni = i + di; nj = j + dj
            if 0 <= ni <= H-1 and 0 <= nj <= W-1 and visited[ni][nj] == 0:
                visited[ni][nj] = 1
                ntr = tr[:]; ntr.append([ni,nj])
                q.append([ni,nj,ntr])

def change(tr):
    def func(d):
        if d == (1,0):return "U"
        if d == (-1,0):return "D"
        if d == (0,-1):return "L"
        if d == (0,1):return "R"
    for i in range(len(tr)-1):
        (ni,nj) = (tr[i+1][0],tr[i+1][1])
        (i,j) = (tr[i][0],tr[i][1])
        d = (ni-i,nj-j)
        ans_list.append(func(d))

res = []
for i in range(4):
    if i == 0:
        res += bfs(sy,sx,ty,tx)
    else:
        res = res[:-1] + bfs(sy,sx,ty,tx)
    visited = [[0]*W for i in range(H)]
    for i,j in res:
        visited[i][j] = 1
    sy,ty = ty,sy; sx,tx = tx,sx
    visited[ty][tx] = 0

change(res)
ans = "".join(ans_list)
print(ans)

Fixed submission:
sx,sy,tx,ty = map(int,input().split())
(tx,ty) = (tx-sx,ty-sy)
route1 = "U"*ty + "R"*tx
route2 = "D"*ty + "L"*tx
route3 = "L" + "U"*(ty+1) + "R"*(tx+1) + "D"
route4 = "R" + "D"*(ty+1) + "L"*(tx+1) + "U"
ans = route1 + route2 + route3 + route4
print(ans)