Just don't forget to update `dp[0]`

```
class Solution(object):
def minPathSum(self, grid):
"""
:type grid: List[List[int]]
:rtype: int
"""
if len(grid) == 0:
return 0
dp = [0 for _ in xrange(0, len(grid[0]))]
dp[0] = grid[0][0]
for j in xrange(1, len(grid[0])):
dp[j] = dp[j - 1] + grid[0][j]
for i in xrange(1, len(grid)):
pre = dp[0] + grid[i][0]
for j in xrange(1, len(grid[0])):
dp[j] = min(dp[j], pre) + grid[i][j]
pre = dp[j]
dp[0] += grid[i][0]
return dp[-1]
```