#pragma GCC optimize("O3")
#include "dna.h"
#include <bits/stdc++.h>
using namespace std;
string s, c;
const int sz = 100005;
int pref_diff[sz], pref_A_s[sz], pref_A_c[sz];
void init(string a, string b){
s = a;
c = b;
int n = s.size();
pref_diff[0] = (s[0] != c[0]);
pref_A_s[0] = (s[0] == 'A');
pref_A_c[0] = (c[0] == 'A');
for (int i = 1; i < n; ++i) {
pref_diff[i] = pref_diff[i-1] + (s[i] != c[i]);
pref_A_s[i] = pref_A_s[i-1] + (s[i] == 'A');
pref_A_c[i] = pref_A_c[i-1] + (c[i] == 'A');
}
}
int get_distance(int x, int y){
int a1 = pref_A_s[y] - (x > 0 ? pref_A_s[x-1] : 0);
int a2 = pref_A_c[y] - (x > 0 ? pref_A_c[x-1] : 0);
if (a1 != a2) return -1;
bool match = true;
for (int i = x; i <= y; ++i) {
if (s[i] != c[i]) {
match = false;
break;
}
}
if (match) return 0;
int mismatch = pref_diff[y] - (x > 0 ? pref_diff[x-1] : 0);
return (mismatch + 1) / 2;
}
