| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 894722 | beaboss | Building 4 (JOI20_building4) | C++14 | 0 ms | 0 KiB |
This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
// Source: https://oj.uz/problem/view/JOI20_building4
//
#include "bits/stdc++.h"
using namespace std;
#define s second
#define f first
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<pii> vpii;
typedef vector<int> vi;
#define FOR(i, a, b) for (int i = (a); i<b; i++)
bool ckmin(int& a, int b){ return b < a ? a = b, true : false; }
bool ckmax(int& a, int b){ return b > a ? a = b, true : false; }
const int N = (5e5 + 10) * 2;
int a[N];
int b[N];
int c[N];
int oc[N];
int swaps[N]; // -1 if not possible, 1 if dependent, 2 if independent
int cnt = 0;
bool flipped=false;
int n;
char rev(char ff) {
if (ff == 'A') {
cnt--;
return 'B';
}
else {
cnt++;
return 'A';
}
}
string chk(string s) {
if (flipped) {
FOR(i, 0, n) s[i] = rev(s[i]);
}
int prv = -1;
FOR(i, 0, n) {
if (s[i] == 'A') {
assert(a[i] >= prv);
prv = a[i];
} else {
assert(b[i] >= prv);
prv = b[i];
}
}
return s;
}
int count(int s, char c) {
int res = 0;
FOR(i, 0, n) if (c == s[i]) res++;
return res;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n;
n *= 2;
FOR(i, 0, n) {
cin >> a[i];
}
FOR(i, 0, n) cin >> b[i];
string ans;
c[0] = min(a[0], b[0]);
oc[0] = max(a[0], b[0]);
if (c[0] == a[0]) {
cnt++;
ans += 'A';
}
else ans += 'B';
for (int i = 1; i < n; i++) {
if (min(a[i], b[i]) >= c[i-1]) {
c[i] = min(a[i], b[i]);
oc[i] = max(a[i], b[i]);
} else if (max(a[i], b[i]) >= c[i-1]) {
swaps[i]=-1;
c[i] = max(a[i], b[i]);
oc[i] = min(a[i], b[i]);
} else {
cout << -1 << endl;
return 0;
}
if (c[i] == a[i]) {
cnt++;
ans += 'A';
}
else ans += 'B';
}
if (cnt == n/2) {
cout << ans << endl;
return 0;
}
if (cnt > n/2) {
flipped=true;
FOR(i, 0, n) ans[i] = rev(ans[i]);
}
c[n] = 1e9 + 10;
for (int i = n-1; i >= 0; i--) {
assert(c[i] <= c[i+1]);
if (swaps[i] == -1) continue;
if (oc[i] <= c[i + 1]) swaps[i]=2; // independent
else if (swaps[i + 1] != -1 && oc[i] <= oc[i + 1]) swaps[i]=1; // dependent
else swaps[i]=-1;
// cout << i << swaps[i] << endl;
}
int st = n-1;
int mx = -1;
int pos = -1;
int res = 0;
// assumes that A has less frequency
for (int i = n-1; i >= 0; i--) {
// cout << i << st << swaps[i] << endl;
assert(cnt == count(ans, 'A'));
if (swaps[i] == -1 || swaps[i] == 2) {
// cout << i << endl;
if (i != st) {
if (mx != -1) {
// cout << st << pos << endl;
for (int j = st; j >= pos; j--) {
if (cnt != n/2) ans[j] = rev(ans[j]);
else {
cout << chk(ans) << endl;
return 0;
}
if (cnt == n/2) {
cout << chk(ans) << endl;
return 0;
}
}
}
}
st = i-1;
// cout << i << st << endl;
}
if (swaps[i] == 2) {
st = i;
}
if (swaps[i] != -1) {
res -= (ans[i] == 'A');
res += (ans[i] == 'B');
if (res > mx) {
pos = i;
mx = res;
}
}
// cout << i << st << mx << res << ans[i] << endl;
}
if (0 <= st) {
for (int j = st; j >= pos; j--) {
if (cnt != n/2) ans[j] = rev(ans[j]);
else {
cout << chk(ans) << endl;
return 0;
}
}
}
if (cnt == n/2) cout << chk(ans) << endl;
else cout << -1 << endl;
}