32 lines
443 B
Python
32 lines
443 B
Python
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# @ref https://oi.wiki/ds/fenwick
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n=...
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c=[0]*(n+1)
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lowbit=lambda x: x&-x
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def prep(a):
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res=[0]*(n+1)
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s=0
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for i in range(1,n+1):
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s+=a[i]
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res[i]=s
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return res
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def init(a):
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pa=prep(a)
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for i in range(1,n+1):
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c[i]=pa[i]-pa[i-lowbit(i)]
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def getsum(x):
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ans=0
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while x:
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ans+=c[x]
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x-=lowbit(x)
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return ans
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def add(x,k):
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while x<=n:
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c[x]+=k
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x+=lowbit(x)
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