std::erase crash when count duplicate char in a loop? - c++

Question

Segmentation fault is throw in the below code.
Counting total no of duplicate char As examples
input:
helloWorld
output:
l = 3
o = 2
steps
Loop input string
search for each char
count on found
del the counted char
Below is my code
#include<iostream>
#include<string>
#include<bits/stdc++.h>
#include <algorithm>
int main()
{
std::string str;
std::cin>>str;
int cout = 0;
std::string::iterator it1,it2;
for(it1 = str.begin() ; it1!=str.end(); ++it1)
{
for(it2 = str.begin() ; it2!=str.end(); ++it2)
{
if(*it1==*it2)
{
++cout;
continue ;
}
}
if(cout >1)
{
std::cout<<*it1<<"="<<cout<<"\n";
if(!str.empty() && str.find(*it1))
str.erase(std::remove(str.begin(), str.end(), *it1), str.end()); // remove char once count done
}
cout=0;
}
}

Answer 1

Your iterators it1 and it2 are being invalidated when you adjust the string str.
Don't do it like that. Use indexes into the std::string (of std::size_t types) instead.
(I'd solve this using an container foo say of int of size CHAR_MAX - CHAR_MIN + 1, initialised to zero, which is such that foo[i] is the number of times character i occurs. This can be populated in O(N), and the output stage is particularly trivial: see Can the Duplicate Characters in a string be Identified and Quantified in O(n)?)

Answer 2

Use c++'s built in functionality. By using sort and adjacent_find to do this in O(n log n) time:
sort(begin(str), end(str));
for(auto start = adjacent_find(cbegin(str), cend(str)), finish = upper_bound(start, cend(str), *start); start != cend(str); start = adjacent_find(finish, cend(str)), finish = upper_bound(start, cend(str), *start)) {
cout << *start << " = " << distance(start, finish) << endl;
}
Live Example