Buggy python submission (verdict: Time Limit Exceeded):
def cmb(n, r):
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n

    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]

    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot

    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])

    return result

h,w,a,b = map(int,input().split())
res = 0
kai = min(w-b,h-a)
mod = 10**9+7

cmb1 = cmb(h-a-1+b,b) 
cmb2 = cmb(a+w-b-1,a) 
combi = cmb1 * cmb2 
res = combi

for i in range(1,kai):
    combi = (combi *(h-a-i)*(w-b-i))//((b+i)*(a+i))
    res += combi
    res %= mod

print(int(res))

Fixed submission:
h, w, a, b = map(int, input().split())
res = 0
kai = min(w - b, h - a)
mod = 10 ** 9 + 7

kaijo = [0] * (h + w + 1)
kaijo[0] = 1
for i in range(1, h + w + 1):
    kaijo[i] = (kaijo[i - 1] * i) % mod
gyaku = [0] * (h + w + 1)
gyaku[h + w] = pow(kaijo[h + w], mod - 2, mod)
for i in range(h + w, 0, -1):
    gyaku[i - 1] = (gyaku[i] * i) % mod


def conb(x, k):
    return (kaijo[x] * gyaku[k] * gyaku[x - k]) % mod


conb1 = conb(h - a - 1 + b, b)
conb2 = conb(a + w - b - 1, a)
combi = conb1 * conb2
res = combi

for i in range(1, kai):
    res += conb(h - a - 1 + b, b + i) * conb(a + w - b - 1, a + i)

res %= mod
print(int(res))

Buggy python submission (verdict: Time Limit Exceeded):
def cmb(n, r):
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n

    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]

    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot

    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])

    return result

h,w,a,b = map(int,input().split())
res = 0
kai = min(w-b,h-a)
for i in range(0,kai):
    res += (cmb(h-a-1+b,b+i) * cmb(a+w-b-1,a+i) ) % (10**9+7)
    if res  > 10**9+7:
        res %= 10**9+7

print(res)

Fixed submission:
h, w, a, b = map(int, input().split())
res = 0
kai = min(w - b, h - a)
mod = 10 ** 9 + 7

kaijo = [0] * (h + w + 1)
kaijo[0] = 1
for i in range(1, h + w + 1):
    kaijo[i] = (kaijo[i - 1] * i) % mod
gyaku = [0] * (h + w + 1)
gyaku[h + w] = pow(kaijo[h + w], mod - 2, mod)
for i in range(h + w, 0, -1):
    gyaku[i - 1] = (gyaku[i] * i) % mod


def conb(x, k):
    return (kaijo[x] * gyaku[k] * gyaku[x - k]) % mod


conb1 = conb(h - a - 1 + b, b)
conb2 = conb(a + w - b - 1, a)
combi = conb1 * conb2
res = combi

for i in range(1, kai):
    res += conb(h - a - 1 + b, b + i) * conb(a + w - b - 1, a + i)

res %= mod
print(int(res))

Buggy python submission (verdict: Time Limit Exceeded):
h,w,a,b = map(int,input().split())

res = []
for i in range(0,h):
    res.append([0 for i in range(w)])

for i in range(0,w):
    res[0][i] = 1

for j in range(1,h):
    res[j][0] = 1

for i in range(h-a,h):
    for j in range(0,b):
        res[i][j] = -1

for i in range(1,h):
    for j in range(1,w):
        if res[i][j] == -1:
            continue
        elif res[i][j-1] == -1:
            res[i][j] = res[i-1][j]
        else:
            res[i][j] = res[i-1][j] + res[i][j-1]
            if res[i][j] > 10**9+7:
                res[i][j] %= 10**9+7

print(res[h-1][w-1])

Fixed submission:
h, w, a, b = map(int, input().split())
res = 0
kai = min(w - b, h - a)
mod = 10 ** 9 + 7

kaijo = [0] * (h + w + 1)
kaijo[0] = 1
for i in range(1, h + w + 1):
    kaijo[i] = (kaijo[i - 1] * i) % mod
gyaku = [0] * (h + w + 1)
gyaku[h + w] = pow(kaijo[h + w], mod - 2, mod)
for i in range(h + w, 0, -1):
    gyaku[i - 1] = (gyaku[i] * i) % mod


def conb(x, k):
    return (kaijo[x] * gyaku[k] * gyaku[x - k]) % mod


conb1 = conb(h - a - 1 + b, b)
conb2 = conb(a + w - b - 1, a)
combi = conb1 * conb2
res = combi

for i in range(1, kai):
    res += conb(h - a - 1 + b, b + i) * conb(a + w - b - 1, a + i)

res %= mod
print(int(res))