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The "eight queens puzzle" is the problem of placing eight chess queens on an 8 chessboard so that no two queens threaten each other. Thus, a solution 阅读全文
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Recommendation system predicts the preference that a user would give to an item. Now you are asked to program a very simple recommendation system that 阅读全文
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Given a syntax tree (binary), you are supposed to output the corresponding infix expression, with parentheses reflecting the precedences of the operat 阅读全文
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In the big cities, the subway systems always look so complex to the visitors. To give you some sense, the following figure shows the map of Beijing su 阅读全文