https://wiki.cvbbacm.com/ 2026-04-30T02:44:37+0800 https://wiki.cvbbacm.com/ https://wiki.cvbbacm.com/lib/exe/fetch.php?media=favicon.ico text/html 2021-07-16T00:47:36+0800 Anonymous (anonymous@undisclosed.example.com) https://wiki.cvbbacm.com/doku.php?id=2020-2021:teams:legal_string:%E7%8E%8B%E6%99%BA%E5%BD%AA:contest:educational_codeforces_round_111&rev=1626367656&do=diff Educational Codeforces Round 111 比赛链接 D. Excellent Arrays 题意 我们称满足以下条件的数组 $a$ 为好数组 $a_{i} != i,i∈[1,n],n$ 是数组长度 我们规定 $F(a)$ 为一个数组中满足 $1≤i＜j≤n$ 且 $a_{i}+a_{j}=i+j$ 的对数。 再规定完美的数组为好数组且 $l≤a_{i}≤r$ 且它的 $F$ 函数值为所有好数组中最大的那个，给定 $n,l,r$$10^{9}+7$$t$$1≤t≤1000,2≤n≤2·10^{5},-10^{9}≤l≤1,n≤r≤10^{9}$$n$$F$${\frac {n^2} 4}$$a_{i} != i$$x$$n-x$$x×(n-x)$$n$${\frac {n^2} 4}$$1$$1$$n$$1$$[1,n]$$l,r$$n$$1$${\frac n 2}$${\frac n 2}+1$$n$$min({\frac n 2}+1-l,r-{\frac n 2})$$j$$[{\frac n 2},n]$$i$$[1,{\frac n …