Minimum number of deletions and insertions

'''
LCS variation:
for eg s1=heap s2=pea, for reaching from s1 to s2 we need to delete h & p from s1 because h is not in s2 and p is before the 'ea'
so if you observer this you will realise you are converting s1-> LCS(s1,s2) ie. 'ea' and then coverting to the s2
ok, now for converting s1-> LCA, you are doing deletions of ie. len(s1)-len(LCS) chars and then again you are doing
addition of len(s2)-len(LCS) characters.

so find the LCS length and deletions=len(s1)-len(LCS) and insertions=len(s2)-len(LCS) and total modificatoins=insertions+deletions
'''
def fun(s1,s2,n,m,dp):
    if n<0 or m<0:
        return 0
    if dp[n][m]!=-1:
        return dp[n][m]
    if s1[n]==s2[m]:
        dp[n][m]=1+fun(s1,s2,n-1,m-1,dp)
    else:
        dp[n][m]=max(fun(s1,s2,n-1,m,dp), fun(s1,s2,n,m-1,dp))
    return dp[n][m]

class Solution:
    def minOperations(self, s1, s2):
        dp=[[-1]*len(s2) for _ in range(len(s1))]
        ans=fun(s1,s2,len(s1)-1,len(s2)-1,dp)
        deletions=len(s1)-ans
        insertions=len(s2)-ans
        return deletions+insertions