Hello world! Can you help me with this(Word break) problem's time complexity. Actually I always feel difficulty in finding time complexity of memoization solutions.

Below is my accepted code:

class Solution {
public:
    int solve(string s, vector<vector<string>> &v, int i, vector<int> &dp)
    {
        if(i==s.size())
        {
            return 1;
        }
        if(dp[i]!=-1)
            return dp[i];
        char c=s[i];
        if((int)v[c-'a'].size()==1)
        {
            return 0;
        }
        else
        {
            int x=0;
            for(int j=0;j<(int)v[c-'a'].size()-1;j++)
            {
                if(s.substr(i, (int)v[c-'a'][j].size())==v[c-'a'][j])
                {
                    x|=solve(s, v, i+(int)v[c-'a'][j].size(), dp);
                }
            }
            dp[i]=x;
            return x;
        }
    }
    bool wordBreak(string s, vector<string>& wordDict) {
        int n=s.size();
        vector<vector<string>> v(26);
        for(int i=0;i<wordDict.size();i++)
        {
            char c=wordDict[i][0];
            v[c-'a'].push_back(wordDict[i]);
        }
        for(int i=0;i<26;i++)
            v[i].push_back("x");
        vector<int> dp(n+1, -1);
        return solve(s, v, 0, dp);
    }
};

Thank u.