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Codeforces Round #677 (Div. 3) 1433F. Zero Remainder Sum

1406C. Link Cut Centroids题意：给一颗树，定义树的质心为：将质心及质心所连的所有边剔除之后，生成的联通块的大小的最大值最小的点。要求删除一条边，再加入一条边，使得新图仍然是树且质心唯一。思路：通过质心的定义就能够明白树的质心至多2个，且若质心有两个，这两个质心必定是父子节点的关系。那么这个问题就很好解决了，只有两种可能：1.质心只有一个。那么只要不改变树本身的样子，即删除、添加任意的一条边，质心仍然唯一；2.质心有两个。那么只要将两个质心的其中一个质心按照剔除的规则生成的

1388C. Uncle Bogdan and Country Happiness题意：国家有N个城市，1号城市为首都，有M个国民，每个国民都在首都工作，晚上返回家中，给定每个城市有多少国民居住。每个城市都有一个心情检测器，当国民经过城市时，心情检测器根据国民的心情加减1，但是心情检测器并不精确，所以要求你去判断在所有国民回家之后心情检测器上的数值是否正确。思路：肯定是从叶子结点倒着遍历整颗树，从下往上，每个结点都判断是否合法。对于每个结点记录两个量：一个是经过这个结点的人数会有多少(ei数组)，一

1380A. Three Indices1380B. Universal Solution1380C. Create The Teams1380D. Berserk And Fireball

1366A. Shovels and Swords 1366B. Shuffle 1366C. Palindromic Paths 1366D. Two Divisors 1366E. Two Arrays

1374A. Required Remainder1374B. Multiply by 2, divide by 61374C. Move Brackets1374D. Zero Remainder Array1374E1. Reading Books (easy version)

A. C+=B. Codeforces SubsequencesC. Even PictureD. AND, OR and square sum

A. Maximum GCDB. GCD CompressionC. Number GameD. Odd-Even Subsequence

A. XXXXXB. Most socially-distanced subsequenceC. Ehab and Prefix MEXs

1365A. Matrix Game1365B. Trouble Sort1365C. Rotation Matching1365D. Solve The Maze1365E. Maximum Subsequence Value1365F. Swaps Again

A. Johnny and Ancient ComputerB. Johnny and His HobbiesC. Johnny and Another Rating DropD. Johnny and Contribution

A. Phoenix and BalanceB. Phoenix and BeautyC. Phoenix and DistributionD. Phoenix and Science

A. Sum of Odd IntegersB. Princesses and PrincesC. Game with ChipsD. Infinite Path

1371A. Magical Sticks1371B. Magical Calendar1371C. A Cookie for You1371DD. Grid-001001371E1. Asterism (Easy Version)