-
-
Save shakayami/ffb66821f513dede1880870b7be5c05a to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
class fenwick_tree(): | |
n=1 | |
data=[0 for i in range(n)] | |
def __init__(self,N): | |
self.n=N | |
self.data=[0 for i in range(N)] | |
def add(self,p,x): | |
assert 0<=p<self.n,"0<=p<n,p={0},n={1}".format(p,self.n) | |
p+=1 | |
while(p<=self.n): | |
self.data[p-1]+=x | |
p+=p& -p | |
def sum(self,l,r): | |
assert (0<=l and l<=r and r<=self.n),"0<=l<=r<=n,l={0},r={1},n={2}".format(l,r,self.n) | |
return self.sum0(r)-self.sum0(l) | |
def sum0(self,r): | |
s=0 | |
while(r>0): | |
s+=self.data[r-1] | |
r-=r&-r | |
return s | |
N=int(input()) | |
a=[int(i) for i in input().split()] | |
G=fenwick_tree(N) | |
ans=0 | |
for i in range(N): | |
ans+=G.sum(a[i],N) | |
G.add(a[i],1) | |
print(ans) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment