Longest Common Subsequence - DP on Strings

Problem Link:

https://www.codingninjas.com/studio/problems/longest-common-subsequence_624879?utm_source=striver&utm_medium=website&utm_campaign=a_zcoursetuf

My approach:

Code:

int helper(string s, string t, int ind1, int ind2, vector<vector<int>> &dp){

    if(ind1==0 || ind2==0){
        return 0;
    }

    if(dp[ind1][ind2]!=-1){
        return dp[ind1][ind2];
    }

    int ans = 0;

    if(s[ind1-1]==t[ind2-1]){
        ans = 1 + helper(s,t,ind1-1,ind2-1,dp);
    }else{
        int a = helper(s,t,ind1-1,ind2,dp);
        int b = helper(s,t,ind1,ind2-1,dp);

        ans = max(a,b);
    }

    dp[ind1][ind2] = ans;
    return ans;

}

int lcs(string s, string t)
{
    //Write your code here

    int n = s.size();
    int m = t.size();

    vector<vector<int>> dp(n+1, vector<int>(m+1,-1));
    return helper(s,t,n,m,dp);
}