#include "dna.h"
#include <bits/stdc++.h>
#define ll long long int
using namespace std;
string a, b; int n;
vector<ll> as, bs;
// A = 0, T = 1
void init(string aa, string bb) {
a = aa; b = bb; n = a.size();
as.resize(n); bs.resize(n);
if (a[0] == 'T') as[0]++;
if (b[0] == 'T') bs[0]++;
for (int i = 1; i < n; i++) {
as[i] = as[i-1];
bs[i] = bs[i-1];
if (a[i] == 'T') as[i]++;
if (b[i] == 'T') bs[i]++;
}
}
int get_distance(int x, int y) {
ll suma = as[y], sumb = bs[y];
if (x > 0) {
suma -= as[x-1]; sumb -= bs[x-1];
}
if (suma != sumb) return -1;
int cnt = 0;
for (int i = x; i <= y; i++) {
if (a[i] != b[i]) cnt++;
}
return cnt/2;
}
