Lib/転倒数

code:cpp

void zaatu(vector<int> &vec){

vector<int> tmp_vec(vec.size());

ll n = vec.size();

sort(tmp_vec.begin(),tmp_vec.end());

map<int,int> mp;

int cnt = 0;

rep(i,n){

cnt++;

}

}

}

ll inv_num(vector<ll> v){

ll n = v.size();

zaatu(v);

auto op = [](ll a,ll b){return a+b;};

auto e = [](){return 0;};

atcoder:segtree<ll,op,e> seg(n+1);

ll ans = 0;

for(ll val : v){

ans += seg.prod(val+1,n+1);

seg.set(val,seg.get(val)+1);

}

return ans;

}

Use:

validate: