摘要：最简单的就是变成1~n的序列； 我们可以先加一个极大的数防止出现负数； 然后对于每一个%(a[ i ] - i)； 阅读全文

摘要：For each string s consisting of characters '0' and '1' one can define four integers a00, a01, a10 and a11, where axy is the number of subsequences of 阅读全文

摘要：Mahmoud was trying to solve the vertex cover problem on trees. The problem statement is: Given an undirected tree consisting of n nodes, find the mini 阅读全文