Longest Common Subsequence

Revision en2, by R.A.N.K.A., 2020-04-27 09:02:45

Can anyone help me out.

why this code is giving time limit error(tle):

int fun(vector<vector<int> > &dp,int i,int j,string s1,string s2)
{
if(i==s1.length()|| j==s2.length()) return 0;
int &ans=dp[i][j];
if(ans!=-1) return ans;
ans=max(fun(dp,i,j+1,s1,s2),fun(dp,i+1,j,s1,s2));
if(s1[i]==s2[j])
ans=max(ans,1+fun(dp,i+1,j+1,s1,s2));
return ans;
}

int Solution::solve(string s1, string s2) {
if(!s1.length() || !s2.length())    return 0;
int n=s1.size(),m=s2.size();
vector<vector<int> > dp(n,vector<int> (m,-1));
return fun(dp,0,0,s1,s2);
}


and why this code get accepted:

×

int Solution::solve(string s1, string s2) {
if(!s1.length() || !s2.length())    return 0;
int n=s1.size(),m=s2.size(),i,j;
vector<vector<int> > dp(n+1,vector<int> (m+1,0));
for(i=1;i<=n;i++)
for(j=1;j<=m;j++)
{
if(s1[i-1]==s2[j-1])
dp[i][j]=1+dp[i-1][j-1];
else
dp[i][j]=max(dp[i-1][j],dp[i][j-1]);
}
return dp[n][m];
}


both solutions have time complexity O(m*n) memoization gives tle and tabulation passes the constraints why?? Thanks in advance.

#### History

Revisions

Rev. Lang. By When Δ Comment
en2 R.A.N.K.A. 2020-04-27 09:02:45 46
en1 R.A.N.K.A. 2020-04-27 09:01:19 1370 Initial revision (published)