with 1D array,record the left_top

```
class Solution:
# @return an integer
def minDistance(self, word1, word2):
m,n = len(word1), len(word2)
if m == 0 : return n
if n == 0 : return m
edit = [j for j in range(n+1)]
for i in range(1, m+1):
left_top, edit[0] = edit[0], i
for j in range(1, n+1):
left_top, edit[j] = edit[j], min( edit[j] + 1, edit[j - 1] + 1, left_top + (0 if word1[i-1] == word2[j-1] else 1))
return edit[n]
```