#include "dna.h"
#include <bits/stdc++.h>
using namespace std;
#define tii array<int,3>
vector<tii> cnt1, cnt2;
int n;
vector<int> dif;
int cnv(char c) {
if (c == 'A') return 0;
if (c == 'C') return 1;
return 2;
}
tii operator-(const tii &x, const tii &y) {
return {x[0]-y[0], x[1]-y[1], x[2]-y[2]};
}
void ii(string a, vector<tii> &cnt) {
cnt[0][cnv(a[0])]++;
for (int i=1;i<n;i++) {
cnt[i] = cnt[i-1];
cnt[i][cnv(a[i])]++;
}
}
void init(string a, string b) {
n = (int)a.size();
cnt1.assign(n, {0, 0, 0});
cnt2.assign(n, {0, 0, 0});
ii(a, cnt1);
ii(b, cnt2);
dif.assign(n, 0);
for (int i=0;i<n;i++) {
if (a[i] != b[i]) dif[i]++;
}
for (int i=1;i<n;i++) {
dif[i] += dif[i-1];
}
}
int get_distance(int x, int y) {
// first check count
tii t1 = cnt1[y];
if (x) {
t1 = t1 - cnt1[x-1];
}
tii t2 = cnt2[y];
if (x) {
t2 = t2 - cnt2[x-1];
}
if (t1 != t2) {
return -1;
}
int df = dif[y];
if (x) {
df -= dif[x-1];
}
df = (df/2) + (df%2);
return df;
}
