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March 5, 2019 02:42
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NOIC - Ideia 01 - Exemplo 1
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// NOIC - Ideia 1 | |
// Exemplo 1 | |
// Complexidade: O(N log N) | |
#include <bits/stdc++.h> | |
using namespace std; | |
const int maxn = 1e5+10; | |
int n, V[maxn], bit[maxn]; | |
// somar v na posição x | |
void upd(int x, int v) | |
{ | |
for (; x <= n; x += (x&-x)) | |
bit[x] += v; | |
} | |
// soma de 1 até x | |
int soma(int x) | |
{ | |
int ans = 0; | |
for (; x > 0; x -= (x&-x)) | |
ans += bit[x]; | |
return ans; | |
} | |
int main(void) | |
{ | |
cin >> n; | |
vector<int> C; // vetor auxiliar | |
for (int i = 1; i <= n; i++) | |
{ | |
cin >> V[i]; | |
C.push_back(V[i]); | |
} | |
sort(C.begin(), C.end()); // ordenamos C | |
int ind = 0; | |
map<int, int> Mp; | |
for (int i = 0; i < C.size(); i++) | |
if (Mp.find(C[i]) == Mp.end()) // se C[i] não foi mapeado ainda | |
Mp[C[i]] = ++ind; // valor mapeado de C[i] | |
long long ans = 0; // resposta (que pode chegar a long long) | |
for (int i = n; i >= 1; i--) | |
{ | |
// a partir de agora trocamos os V[i]s pelos seus valores mapeados | |
ans += soma(Mp[V[i]]-1); // inversões que i participa | |
upd(Mp[V[i]], 1); | |
} | |
cout << ans << "\n"; | |
} |
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