使用SET（C ++）检查两个给定的字符串是否为字谜时出现运行时错误

Question

Link to the problem: https://www.hackerearth.com/practice/basic-programming/input-output/basics-of-input-output/practice-problems/algorithm/two-strings-4/

I have started with set and map these days. Two strings str1 and str2 have equal length. I have to tell if they are anagrams of each other. I used unordered_map to solve the problem by maintaining the count of characters which works in linear time and is great. But I want to use unordered_multiset but i am getting a run-time error.

code:

#include<bits/stdc++.h>
using namespace std;
int main(){ 
int t;// number of testcases
cin>>t;
while(t--){
    string str1,str2;// two strings of equal length str1 and str2
    cin>>str1>>str2;
    unordered_multiset<char> s1,s2;// two sets 
    for(int i=0;i<str1.length();i++){
        s1.insert(str1[i]);// initialization
        s2.insert(str2[i]);
    }
    unordered_multiset<char>::iterator itr;
    for(itr=s1.begin();itr!=s1.end();itr++){
        if(s2.find(*itr)!=s2.end()) s2.erase(itr);/*  if *itr is present in s2 then delete its address .....
                                                    i know i am making mistake somewhere here but i can't figure out*/
        else {
            cout<<"NO"<<"\n";// print NO if not found
            break;
        }
    }
    if(itr==s1.end()) cout<<"YES"<<"\n";// if itr reached the end print YES
}
}

The idea is to loop through the set s1 and find the corresponding element in the set s2. If not found print NO and break otherwise delete the corresponding element from s2 and since i am using iterator to delete elements so if there are multiple occurrences of a character then 1st occurrence should be deleted.

please let me know if you didn't get my question

Answer 1

Try to solve it in a simpler way. The problem states that there are only lowercase characters, you can use only a frequency array for each word, an then compare it.

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int t;
    cin >> t;
    while(t--)
    {
        vector<int> f1(26, 0);
        vector<int> f2(26, 0);
        string s1, s2;
        cin >> s1 >> s2;
        for(const char& c : s1) f1[c - 'a']++;
        for(const char& c : s2) f2[c - 'a']++;
        cout << ( (f1 == f2)? "YES" : "NO") << endl;
    }
}

Answer 2

It's because you are using the iterator from s1 to erase an element from s2:

if(s2.find(*itr)!=s2.end()) s2.erase(itr);

It have to be like this:

if(s2.find(*itr)!=s2.end()) s2.erase(*itr);

or:

auto elem = s2.find(*itr);
if (elem != s2.end())
   s2.erase(elem);