Created
March 8, 2014 04:42
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Chef and Reunion
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#include <iostream> | |
#include <vector> | |
#include <map> | |
#include <algorithm> | |
using namespace std; | |
int ac [100000]; | |
void update(int ix, int val, int n){ | |
int nv = val; | |
for(; ix < n + 1; ix += (ix & -ix)) | |
ac[ix] += val; | |
} | |
int query(int ix){ | |
int r = 0; | |
while(ix){ | |
r += ac[ix]; | |
ix -= (ix & -ix); | |
} | |
return r; | |
} | |
struct par{ | |
int M; | |
int F; | |
}; | |
inline bool operator<(const par& a, const par& b) | |
{ | |
return a.M < b.M; | |
} | |
int main(){ | |
int N, n; | |
int m, f; | |
cin >> N; | |
n = N; | |
vector<par> parejas; | |
vector<int> fem; | |
map<int, int> mapa; | |
while(N--){ | |
cin >> m >> f; | |
par p; | |
p.M = m; | |
p.F = f; | |
parejas.insert(parejas.end(),p); | |
fem.insert(fem.end(),f); | |
} | |
std::sort (fem.begin(), fem.end()); | |
std::sort (parejas.begin(), parejas.end()); | |
for(int i = 0; i < n; i++){ | |
mapa[fem[i]] = i+1; | |
} | |
for(int i = 1; i < n+1; i++){ | |
update(mapa[parejas[i-1].F],1,n); | |
} | |
long long int res = 0; | |
for(int i = 0; i < n; i++){ | |
res += query(mapa[parejas[i].F]) - 1; | |
update(mapa[parejas[i].F],-1,n); | |
} | |
cout << res << endl; | |
return 0; | |
} |
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