2018 ACM-ICPC 瀋陽網路賽C Convex hull 阿新 • • 發佈:2019-01-28 考慮杜教篩就跑偏了… 定義gay(i)=i2∗μ2(i)gay(i)=i2∗μ2(i) ∑ni=1∑ij=1gay(i)=∑ni=1(n−i+1)gay(i)=∑ni=1(n−i+1)i2μ2(i)∑i=1n∑j=1igay(i)=∑i=1n(n−i+1)gay(i)=∑i=1n(n−i+1)i2μ2(i) 有μ2(n)=∑i2|nμ(i)μ2(n)=∑i2|nμ(i) 因此上式 =∑ni=1(n−i+1)i2(∑j2|iμ(j))=∑i=1n(n−i+1)i2(∑j2|iμ(j)) 列舉因子變成列舉倍數 ∑ni=1(n−i+1)i2(∑j2|iμ(j))=∑n√i=1μ(i)(∑ ⌊ni2⌋j=1(n−i2j+1)i4j2)=∑n√i=1μ(i)(∑⌊ni2⌋j=1(i4j2(n+1)−i6j3))∑i=1n(n−i+1)i2(∑j2|iμ(j))=∑i=1nμ(i)(∑j=1⌊ni2⌋(n−i2j+1)i4j2)=∑i=1nμ(i)(∑j=1⌊ni2⌋(i4j2(n+1)−i6j3)) ∑ni=1i2=n∗(n+1)∗(2n+1)6,∑ni=1i3=n2(n+1)24∑i=1ni2=n∗(n+1)∗(2n+1)6,∑