```
def minDistance(self, A, B):
"""
:type A: str
:type B: str
:rtype: int
"""
m,n=len(A),len(B)
dp=[[0 for _ in xrange(n+1)] for _ in xrange(m+1)]
for i in xrange(1,m+1):
for j in xrange(1,n+1):
if A[i-1]==B[j-1]:
dp[i][j]=dp[i-1][j-1]+1
else:
dp[i][j]=max(dp[i-1][j],dp[i][j-1])
res=m-dp[m][n]+n-dp[m][n]
return res
```