随笔分类 - Atcoder
摘要：题目链接 考虑最后形态，一定是有某一个区间 \([l,r]\) 保持初始的样子， \(l\) 前面都是 <，\(r\) 后面都是 >。 这个区间一定是某两个相邻圆点的位置。设 \(f_i\) 为前 \(i\) 个数全部被覆盖成 < 的概率。设 \(x\) 为 \(l\) 前面圆点的数量，\(y\)
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摘要：题解链接 非常厉害的一道题。 考虑无解是什么情况？ R 的个数超过 \(2^{n-1}\) 先考虑如何判定。从前往后考虑，如果遇到一个 B，那么如果后面有 R，就选最靠前的 R，否则选最靠后的一个 B.如果遇到 R，就选最靠后的一个 B。 但是这个判定很繁琐。我们考虑求出一个合法序列，使得他的 B
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摘要：题目链接 好题。 如果 \(1\) 和 \(n\) 一直联通，开始即结束。 如果 \(n\mod 4=1\)，那么 \(\frac 12x(x+1)+\frac12(n-x)(n-x+1)\) 为偶数。 如果 \(n\mod 4=3\)，那么 \(\frac 12x(x+1)+\frac12(n-x
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摘要：题目链接 简化题意：有一个 \(n\) 个点的图，问有多少个长度为 \(M\) 的边序列，满足连边后图是二分图。 \(n\le 30,m\le 10^9\) 考虑先强制要求无重边。 定义 \(f_{i,j}\) 为 \(i\) 个点，\(j\) 条边的图的二分图染色数量（染色方式不同算多次）。这个是
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摘要：题目链接 看到严格选 \(k\) 个，不难想到 WQS二分。定义 \(f(x)\) 为分成 \(x\) 段，最多有多少个超过 \(S\) 的。然后你会发现他不是凸的。因为他有很多平段，比如把两个很小的合并不改变答案。 换个方向？ 考虑定义 \(f(x)\) 为有 \(x\) 个超过 \(S\) 的段
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摘要：Problem StatementWe have a sequence of $N$ positive integers: $A_1,A_2,\cdots,A_N$. You are to rearrange these integers into another sequence $x_1,x_2
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摘要：Problem StatementThere are $2N$ integers written on a blackboard. The $i$-th integer is $A_i$. Alice and Bob will play a game consisting of $N$ rounds
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摘要：Problem StatementSnuke runs a bakery. He is planning for the next $N$ days. Let us call these days Day $1,2,\cdots,N$. At the moment, the bakery hires
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摘要：Problem StatementYou are given an integer sequence of length $N$: $A_1,A_2,...,A_N$. Let us perform $Q$ operations in order. The $i$-th operation is d
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摘要：Problem StatementThere is a tree with $N$ vertices numbered $1$ to $N$. The $i$-th edge connects vertices $A_i$ and $B_i$. Let us keep performing the
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摘要：Problem StatementFor an integer sequence $X=(X_1,X_2,\dots,X_n)$, let $X[L,R]$ denote the integer sequence $(X_L,X_{L+1},\dots,X_{R})$. You are given
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摘要：Problem StatementWe have a grid with $N$ rows and $M$ columns. We denote by $(i,j)$ the cell in the $i$-th row from the top and $j$-th column from the
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摘要：Problem StatementSnuke got positive integers $s_1,...,s_N$ from his mother, as a birthday present. There may be duplicate elements. He will circle som
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摘要：Problem StatementThere is a grid with $N$ rows and $M$ columns. The square at the $i$-th row from the top and the $j$-th column from the left contains
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摘要：Problem StatementYou are given a simple connected undirected graph $G$ with $N$ vertices and $M$ edges. The vertices and edges of $G$ are numbered as
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摘要：Problem StatementThere are $N$ cards numbered $1$ through $N$. Each face of a card has an integer written on it; card $i$ has $A_i$ on its front and $
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摘要：Problem StatementThere are $2^N$ players, numbered $1, 2, ..., 2^N$. They decided to hold a tournament. The tournament proceeds as follows: Choose a p
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摘要：Problem StatementYou are given a set $S$ of strings consisting of 0 and 1, and an integer $K$. Find the longest string that is a subsequence of $K$ or
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摘要：Problem StatementWe have a sequence of positive integers of length $N^2$, $A=(A_1,\ A_2,\ \dots,\ A_{N^2})$, and a positive integer $S$. For this sequ
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摘要：Problem StatementFind the number, modulo $998244353$, of permutations $P=(P_1,P_2,\dots,P_N)$ of $(1,2,\dots,N)$ such that: $|P_i - i| \ge X$ for all
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