class Solution:
def minDistance(self, strWord1, strWord2):
res = [[0]*(len(strWord2)+1) for _ in range(len(strWord1)+1)]
# handle extreme conditions first
res[len(strWord1)][len(strWord2)] = 0
for j in range(len(strWord2)+1):
res[len(strWord1)][j] = len(strWord2)-j
for i in range(len(strWord1)+1):
res[i][len(strWord2)] = len(strWord1)-i
for i in range(len(strWord1), -1, -1):
for j in range(len(strWord2), -1, -1):
if i == len(strWord1) or j == len(strWord2):
continue
d = 0
if strWord1[i]==strWord2[j]:
d = res[i+1][j+1]
else:
d = min(res[i][j+1], res[i+1][j], res[i+1][j+1]) + 1
res[i][j] = d
return res[0][0]
