POJ 3126 Prime Path 素数筛，bfs

题目： http://poj.org/problem?id=3126

困得不行了，没想到敲完一遍直接就A了，16ms，debug环节都没进行。人品啊。

 1 #include <stdio.h>

 2 #include <string.h>

 3 #include <queue>

 4 using namespace std;

 5 

 6 bool prime[10000];

 7 int vis[10000];

 8 int s, t;

 9 

10 void prime_init()

11 {

12     memset(prime, 1, sizeof(prime));

13     prime[1] = 0;

14     for(int i = 4; i < 10000; i += 2)

15         prime[i] = 0;

16     for(int i = 3; i < 100; i += 2)

17     {

18         if(prime[i])

19         {

20             for(int j = i*i; j < 10000; j += i+i)

21                 prime[j] = 0;

22         }

23     }

24 }

25 

26 queue<int>q;

27 void bfs()

28 {

29     while(!q.empty())q.pop();

30     memset(vis, 0, sizeof(vis));

31     q.push(s);

32     vis[s] = 1;

33     while(!q.empty())

34     {

35         int u = q.front();

36         q.pop();

37         if(u == t)

38         {

39             printf("%d\n", vis[u]-1);

40             return;

41         }

42         int a = u % 10;

43         int b = u % 100 - a;

44         int c = u % 1000 - a - b;

45         int d = u - u % 1000;

46         for(int i = u-a; i <= u-a+9; i++)

47         {

48             if(prime[i] && !vis[i])

49             {

50                 q.push(i);

51                 vis[i] = vis[u] + 1;

52             }

53         }

54         for(int i = u-b; i <= u-b+90; i += 10)

55         {

56             if(prime[i] && !vis[i])

57             {

58                 q.push(i);

59                 vis[i] = vis[u] + 1;

60             }

61         }

62         for(int i = u-c; i <= u-c+900; i += 100)

63         {

64             if(prime[i] && !vis[i])

65             {

66                 q.push(i);

67                 vis[i] = vis[u] + 1;

68             }

69         }

70         for(int i = u-d+1000; i <= u-b+9000; i += 1000)

71         {

72             if(prime[i] && !vis[i])

73             {

74                 q.push(i);

75                 vis[i] = vis[u] + 1;

76             }

77         }

78     }

79 }

80 

81 int main()

82 {

83     prime_init();

84     int n;

85     scanf("%d", &n);

86     while(n--)

87     {

88         scanf("%d %d", &s, &t);

89         bfs();

90     }

91     return 0;

92 }

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