https://www.acmicpc.net/problem/7578
#pragma GCC optimize ("O3")
#include <bits/stdc++.h>
#define fastio ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define int int64_t
using namespace std;
template<typename T = int64_t, size_t sz = 17, typename F = plus<T>>
struct SegTree {
vector<T> tree; T t; F f{};
SegTree(T t = T()) : tree(1 << sz + 1, t), t(t) {}
explicit SegTree(T t, const F& f) : tree(1 << sz + 1, t), t(t), f(f) {}
void Init() {
for (int i = (1 << sz) - 1; i; i--) {
tree[i] = f(tree[i << 1], tree[i << 1 | 1]);
}
}
void Update(int i, T val) {
--i |= 1 << sz; tree[i] = val;
while (i >>= 1) tree[i] = f(tree[i << 1], tree[i << 1 | 1]);
}
T Query(int l, int r) {
T L = t, R = t; --l |= 1 << sz, --r |= 1 << sz;
while (l <= r) {
if (l & 1) L = f(L, tree[l++]);
if (~r & 1) R = f(tree[r--], R);
l >>= 1, r >>= 1;
}
return f(L, R);
}
};
int check[1000001];
int32_t main() {
fastio;
SegTree<int,20> ST;
int n,ans = 0; cin >> n;
for(int i = 1; i <= n; i++){
int t; cin >> t;
check[t] = i;
}
for(int i = 1; i <= n; i++){
int t; cin >> t;
ans += (check[t] - 1 - ST.Query(1,check[t] - 1));
ST.Update(check[t], 1);
}
cout << ans << "\n";
}
#pragma GCC optimize ("O3")
#include <bits/stdc++.h>
#define fastio ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define int int64_t
using namespace std;
int check[1 << 20];
template<typename T = int64_t, size_t sz = 17, typename F = plus<T>>
struct SegTree {
vector<T> tree; T t; F f{};
SegTree(T t = T()) : tree(1 << sz + 1, t), t(t) {}
explicit SegTree(T t, const F& f) : tree(1 << sz + 1, t), t(t), f(f) {}
void Init() {
for (int i = (1 << sz) - 1; i; i--) {
tree[i] = f(tree[i << 1], tree[i << 1 | 1]);
}
}
void Update(int i, T val) {
--i |= 1 << sz; tree[i] = val;
while (i >>= 1) tree[i] = f(tree[i << 1], tree[i << 1 | 1]);
}
T Query(int l, int r) {
T L = t, R = t; --l |= 1 << sz, --r |= 1 << sz;
while (l <= r) {
if (l & 1) L = f(L, tree[l++]);
if (~r & 1) R = f(tree[r--], R);
l >>= 1, r >>= 1;
}
return f(L, R);
}
};
int32_t main() {
fastio;
SegTree<int,20> ST;
int n,r = 0; cin >> n;
for(int i = 1; i <= n; i++){
int t; cin >> t;
check[t] = i;
}
for(int i = 1; i <= n; i++){
int t; cin >> t;
r += (check[t] - 1 - ST.Query(1, check[t] - 1));
ST.Update(check[t], 1);
}
cout << r << "\n";
}
세그먼트 트리에서 inversion counting을 구하는 약간 응용된 문제입니다
첫번째 줄을 입력 받으면서 check배열에 해당 숫자가 몇번째로 나왔는지 저장하고 두번째 줄을 입력 받으면서 check배열의 inversion counting을 구해주면 됩니다.