Error Correct System.cpp

#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cstring>
#include <climits>
#include <stdlib.h>
#include <stdio.h>
using namespace std;
#define REP(i,n) for(int i=0; i<n; i++)
#define FOR(i,st,end) for(int i=st;i<end;i++)
#define db(x) cout << (#x) << " = " << x << endl;
#define mp make_pair
#define pb push_back
#define MAX 100005
typedef long long int ll;

int main(){
	int n;
	string str1,str2;
	cin>>n;
	cin>>str1>>str2;
	//This 2D array is used to store mismatched characters from String S and String T respectively which are in the same index
	//if sameIndex[0][1]=1 then it means 'a' from String S and 'b' from String T are in same index
	//if sameIndex[1][0]=1 then it means 'b' from S and 'a' from T are in same index
	int sameIndex[26][26]={0};
	//The below array is used to store the indexes of the mismatched characters in string T
	//NOTE: String S and T are represented by str1 and str2 in the code and comments from now on 
	int match[26];
	int ham=0;
	int f=0;
	pair<int,int> ans;
	memset(match,-1,sizeof match);
	REP(i,n){
		sameIndex[str1[i]-'a'][str2[i]-'a']=1;
		if(str1[i]!=str2[i]){
			match[str2[i]-'a']=i;
			ham++;
		}
	}
	REP(i,n){
		if(str1[i]!=str2[i]){
			//Case 1
			//If characters str1[i] and str2[i] are different
			//check if character str2[i] in string str1 and str1[i] in string str2 are present in same index 
			//if present then the 2 characters can be swapped and thus hamming distance will be decremented by 2
			if(sameIndex[str2[i]-'a'][str1[i]-'a']){
				ham-=2;
				f=1;
				REP(j,n){
					if(str1[j]==str2[i]&&str2[j]==str1[i]){
						ans.first=i+1;
						ans.second=j+1;
						break;
					}
						
				}
				break;
			}
		}
	}
	if(!f){
		REP(i,n){
			//Case 2
			//check if mismatched character belonging to str1 is present in mismatched character set of str2
			//if present then we can swap str1[i] with the index where str1[i] is present in str2
			if(str1[i]!=str2[i]){
				if(match[str1[i]-'a']!=-1){
					f=1;
					ans.first=i+1;
					ans.second=match[str1[i]-'a']+1;
					ham--;
						break;
				}
					
			}
		}
	}
	
		cout<<ham<<endl;
	if(f){
		cout<<ans.first<<" "<<ans.second<<endl;
	}
	else{
		cout<<"-1 -1";
	}
	
}