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  • HDU 1016 Prime Ring Problem(DFS)

    题目链接

    Problem Description
    A ring is compose of n circles as shown in diagram. Put natural number 1, 2, ..., n into each circle separately, and the sum of numbers in two adjacent circles should be a prime.

    Note: the number of first circle should always be 1.

     
    Input
    n (0 < n < 20).
     
    Output
    The output format is shown as sample below. Each row represents a series of circle numbers in the ring beginning from 1 clockwisely and anticlockwisely. The order of numbers must satisfy the above requirements. Print solutions in lexicographical order.

    You are to write a program that completes above process.

    Print a blank line after each case.
    Sample Input
    6
    8
     
    Sample Output
    Case 1:
    1 4 3 2 5 6
    1 6 5 2 3 4
     
     
    Case 2:
    1 2 3 8 5 6 7 4
    1 2 5 8 3 4 7 6
    1 4 7 6 5 8 3 2
    1 6 7 4 3 8 5 2
     
    题解:一个素数环问题,dfs去遍历所有可能,为了避免重复,把1固定当做第一个数字。前n-1个数字这样判断:1-n循环,如果没有使用过,并且和前一个数字之和是素数,就填进去。最后一个数字,扫描vis数组,哪个没用过就填进去,判断与前后数字是否和为素数,是则输出数组。素数判定可以打表,到40即可。第一发WA,吓死我了==|,仔细一看原来是case没有,注意空行。
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  • 原文地址:https://www.cnblogs.com/gpsx/p/5184810.html
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