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##题目 A binary matrix is called good if every even length square sub-matrix has an odd number of ones. Given a binary matrix a consisting of n rows and 阅读全文
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##题目 Problem Description DZY has a sequence a[1..n]. It is a permutation of integers 1∼n. Now he wants to perform two types of operations: 0lr: Sort a 阅读全文
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##题面 Problem Description John has several lines. The lines are covered on the X axis. Let A is a point which is covered by the most lines. John wants 阅读全文