이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
#include <bits/stdc++.h>
using namespace std;
#define sz(v) int(v.size())
#define ar array
typedef long long ll;
const int N = 5e3+10, MOD = 1e9+7;
const ll INF = 1e18+10;
int n, K, small[N];
ll ps[N], l_use[N];
vector<int> one, two;
// min CHT with
// - slopes decreasing
// - query x increasing
struct Line {
ll m, b;
ll calc(ll x) {
return m * x + b;
}
};
struct CHT {
deque<Line> lines;
void add(ll m, ll b) {
while (sz(lines) >= 2) {
auto A = lines.end()[-2];
auto B = lines.end()[-1];
if ((b - A.b) * (A.m - B.m) <= (B.b - A.b) * (A.m - m)) lines.pop_back();
else break;
}
lines.push_back({m, b});
}
ll qry(ll x) {
while (sz(lines) >= 2 && lines[0].calc(x) >= lines[1].calc(x)) {
lines.pop_front();
}
return lines[0].calc(x);
}
};
void solve() {
cin >> n >> K;
for (int i = 0; i < 2 * n; i++) {
char c; cin >> c;
if (c == 'A') one.push_back(i);
else two.push_back(i);
}
for (int i = 0; i < n; i++) {
small[i] = lower_bound(two.begin(), two.end(), one[i]) - two.begin();
}
for (int i = 0; i < n; i++) {
ps[i] = small[i] + (i ? ps[i-1] : 0);
}
auto calc_sum = [&](int L, int R) {
return (long long) (L + R) * (R - L + 1) / 2;
};
for (int i = 0; i < n; i++) {
l_use[i] = -(i ? ps[i-1] : 0);
for (int j = i; j < n; j++) {
if (small[j] < i) {
l_use[i] -= small[j] - i;
}
}
/*
int use = lower_bound(small, small + n, i) - small - 1; // [i..use]
if (use >= i) {
l_use[i] -= ps[use] - (i ? ps[i-1] : 0) - calc_sum(i, use);
}
*/
}
vector<ll> prv(n, INF);
for (int k = 1; k <= K; k++) {
vector<ll> nxt(n, INF);
CHT lines;
for (int i = 0; i < n; i++) {
lines.add(-i, (long long) i * i - i + l_use[i] + (i == 0 ? 0 : prv[i-1]));
nxt[i] = lines.qry(i) + ps[i];
int l = small[i];
if (l <= i) {
nxt[i] = min(nxt[i], (l == 0 ? 0 : prv[l-1]));
}
}
swap(prv, nxt);
}
cout << prv[n-1] << '\n';
}
int main() {
ios::sync_with_stdio(false); cin.tie(0);
int T = 1;
// cin >> T;
while (T--) solve();
}
컴파일 시 표준 에러 (stderr) 메시지
chorus.cpp: In function 'void solve()':
chorus.cpp:65:10: warning: variable 'calc_sum' set but not used [-Wunused-but-set-variable]
65 | auto calc_sum = [&](int L, int R) {
| ^~~~~~~~
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