在动态规划求解不同路径问题时，下列边界条件与代码实现均正确的是？

def uniquePaths(m, n):
    if m < 1 or n < 1:
        return 
    dp = [[]*n for _ in range(m)]
    for i in range(1, m):
        for j in range(1, n):
            dp[i][j] = dp[i-1][j] + dp[i][j-1]
    return dp[m-1][n-1]

def uniquePaths(m, n):
    if m < 1 or n < 1:
        return 
    dp = [[]*n for _ in range(m)]
    for i in range(m):
        dp[i][] = 1
    for i in range(1, m):
        for j in range(1, n):
            dp[i][j] = dp[i-1][j] + dp[i][j-1]
    return dp[m-1][n-1]

def uniquePaths(m, n):
    if m < 1 or n < 1:
        return 
    dp = [[]*n for _ in range(m)]
    for i in range(m):
        dp[i][] = 1
    for j in range(n):
        dp[][j] = 1
    for i in range(1, m):
        for j in range(1, n):
            dp[i][j] = dp[i-1][j] + dp[i][j-1]
    return dp[m-1][n-1]

def uniquePaths(m, n):
    if m < 1 or n < 1:
        return 
    dp = [[1]*n for _ in range(m)]
    for i in range(1, m):
        for j in range(1, n):
            dp[i][j] = dp[i-1][j] * dp[i][j-1]
    return dp[m-1][n-1]