HDU1016 dfs

刷回溯的时候发现我对DFS思路很不清晰，总是做着做着就乱了，刷个水题找找思路。

题意：经典DFS，找出所有的能让1~n的数形成素数环的序列（相邻相加为素数）；

 1 #include <iostream>
 2 #include <cmath>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <cstdlib>
 6 #include <string>
 7 #include <sstream>
 8 #include <algorithm>
 9 #define Max 2147483647
10 #define INF 0x7fffffff
11 #define ll long long
12 #define mem(a,b) memset(a,b,sizeof(a))
13 #define repu(i, a, b) for(int i = (a); i < (b); i++)
14 const double PI=-acos(-1.0);
15 #define N 10010
16 using namespace std;
17 bool pri[N];
18 int p[N];
19 int prim()
20 {
21     memset(pri, true, sizeof(pri));
22     for(int i = 2; i <= sqrt(60 +0.5); i++)
23         if(pri[i])
24             for(int j = i << 1 ; j <= N; j += i)
25                 pri[j] = false;
26 }
27 int n;
28 bool vis[N];
29 void dfs(int pos,int m)///p[pos-1] = m
30 {
31     if(pos == n+1 && pri[p[n]+1])
32     {
33         repu(i,1,n)
34         printf("%d ",p[i]);
35         printf("%d\n",p[n]);
36         return ;
37     }
38     int i = 2;
39     repu(i,2,n+1)
40     {
41         if(pri[m + i] && !vis[i] )///符合条件
42         {
43             vis[i] = 1;
44             p[pos] = i;
45             dfs(pos+1,p[pos]);
46             vis[i] = 0;
47         }
48     }
49 }
50 int main()
51 {
52     //init();
53     prim();
54     memset(vis,0,sizeof(vis));
55     int kase = 1;
56     while(~scanf("%d",&n))
57     {
58         printf("Case %d:\n",kase++);
59         p[1] = 1;
60         p[n+1] = 1;
61         dfs(2,1);
62         if(kase)
63             printf("\n");
64     }
65     return 0;
66 }
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posted @ 2015-05-22 00:26  一麻袋码的玛侬  阅读(112)  评论(0)  编辑  收藏  举报