I do not know why but when recursion tries to add value and then to return it that map after return of function deletes all elements, I do not understand in what a problem.

static int SumNum(string target, string m[], map<string, int> memo = {}){

        if (memo.find(target) != memo.end()) {
            cout << memo.find(target)->second<<"\n";
            return memo.find(target)->second;
        }
        if (target == "") return 1;

        int totalCount = 0;
        
    for(auto i = 0;i < 10; i  )
    {   
        if (target.find(m[i]) == 0){
            
            int numOfWays = SumNum(target.substr(m[i].length()),m,memo);
            totalCount  = numOfWays;
            
        }
    }
    memo.emplace(target, totalCount);
    return totalCount;
}
int main(){
    string ar[10] = {"e","ee","eee","eeee","eeeee","eeeeee","f","fdc","d","c"};
    string target = "eeeeeeeeefdc";
    auto answer = SumNum(target,ar);
    cout << answer;
}

CodePudding user response：

I think that @Max meant this:

static int SumNum(std::string target, std::string m[], map<string, int>& memo = {} /* pass by reference */){

        if (memo.find(target) != memo.end()) {
            std::cout << memo.find(target)->second<<"\n";
            return memo.find(target)->second;
        }
        if (target == "") return 1;

        int totalCount = 0;
        
    for(auto i = 0;i < 10; i  )
    {   
        if (target.find(m[i]) == 0){
            
            int numOfWays = SumNum(target.substr(m[i].length()),m,memo);
            totalCount  = numOfWays;
            
        }
    }
    memo.emplace(target, totalCount);
    return totalCount;
}
int main(){
    std::string ar[10] = {"e","ee","eee","eeee","eeeee","eeeeee","f","fdc","d","c"};
    std::string target = "eeeeeeeeefdc";
    auto answer = SumNum(target,ar);
    std::cout << answer;
}

CodePudding user response：

thanks @Max i did like you say

static int SumNum(string target, string m[], map<string, int> *memo = new map<string, int>()) {
        
        if (memo->find(target) != memo->end()) {
            cout << memo->find(target)->second<<"\n";
            return memo->find(target)->second;
        }
        if (target == "") return 1;

        int totalCount = 0;
        
    for(auto i = 0;i < 10; i  )
    {   
        if (target.find(m[i]) == 0){
            
            int numOfWays = SumNum(target.substr(m[i].length()),m,memo);
            totalCount  = numOfWays;
            
        }
    }
    memo->emplace(target, totalCount);
    return totalCount;
}
int main(){
    string ar[10] = {"e","ee","eee","eeee","eeeee","eeeeee","f","fdc","d","c"};
    string target = "eeeeeeeeeeeeefdc";
    auto answer = SumNum(target,ar);
    cout << answer;
}