Beautiful IP Addresses
Time Limit: 2000ms
Memory Limit: 262144KB
This problem will be judged on CodeForces. Original ID: 292C
64-bit integer IO format: %I64d Java class name: (Any)
The problem uses a simplified TCP/IP address model, please read the statement carefully.
An IP address is a 32-bit integer, represented as a group of four decimal 8-bit integers (without leading zeroes), separated by commas. For example, record 0.255.1.123 shows a correct IP address and records 0.256.1.123 and 0.255.1.01 do not. In the given problem an arbitrary group of four 8-bit integers is a correct IP address.
Our hero Polycarpus still works as a system administrator in some large corporation. He likes beautiful IP addresses. To check if some IP address is beautiful, he should do the following:
- write out in a line four 8-bit numbers of the IP address, without the commas;
- check if the resulting string is a palindrome.
Let us remind you that a palindrome is a string that reads the same from right to left and from left to right.
For example, IP addresses 12.102.20.121 and 0.3.14.130 are beautiful (as strings "1210220121" and "0314130" are palindromes), and IP addresses 1.20.20.1 and 100.4.4.1 are not.
Polycarpus wants to find all beautiful IP addresses that have the given set of digits. Each digit from the set must occur in the IP address at least once. IP address must not contain any other digits. Help him to cope with this difficult task.
Input
The first line contains a single integer n (1 ≤ n ≤ 10) — the number of digits in the set. The second line contains the set of integers a1, a2, ..., an(0 ≤ ai ≤ 9). It is guaranteed that all digits in the set are distinct.
Output
In the first line print a single integer k — the number of beautiful IP addresses that contain the given set of digits. In the following k lines print the IP addresses, one per line in the arbitrary order.
Sample Input
Input
60 1 2 9 8 7
Output
678.190.209.18779.180.208.19787.190.209.17889.170.207.19897.180.208.17998.170.207.189
Input
14
Output
164.4.4.44.4.4.444.4.44.44.4.44.444.44.4.44.44.4.444.44.44.44.44.44.4444.4.4.444.4.4.4444.4.44.444.4.44.4444.44.4.444.44.4.4444.44.44.444.44.44.44
Source
解题：此题不仅繁琐，而且蛋疼！过滤规则约束难搞。。。。
1 #include <iostream>
2 #include <cstdio>
3 #include <cstring>
4 #include <cstdlib>
5 #include <vector>
6 #include <climits>
7 #include <algorithm>
8 #include <cmath>
9 #define LL long long
10 #define INF 0x3f3f3f
11 using namespace std;
12 int bit[12],n,tot,cnt;
13 bool vis[12];
14 char temp[10000][30],s[30];
15 char ans[10000][60],ss[60];
16 void dfs(int cur,int deep,int kind) {
17 if(cur >= deep) {
18 if(kind == n) {
19 s[cur] = ‘\0‘;
20 strcpy(temp[cnt],s);
21 cnt++;
22 }
23 return;
24 }
25 for(int i = 0; i < n; i++) {
26 s[cur] = bit[i]+‘0‘;
27 if(vis[i]) {
28 dfs(cur+1,deep,kind);
29 } else {
30 vis[i] = true;
31 dfs(cur+1,deep,kind+1);
32 vis[i] = false;
33 }
34 }
35 }
36 void dfs2(char *s,int cur,int p,int len) {
37 int i,j,k,sum = 0,slen = strlen(s);
38 if(cur == 3) {
39 if(p < slen) {
40 for(i = p; i < slen; i++)
41 sum = sum*10+s[i]-‘0‘;
42 if(sum > 255) return;
43 if(s[p] == ‘0‘ && slen-p > 1) return;
44 ss[len] = ‘.‘;
45 for(i = p; i < slen; i++)
46 ss[len+1+i-p] = s[i];
47 ss[len+1+i-p] = ‘\0‘;
48 strcpy(ans[tot++],ss+1);
49 }
50 return;
51 }
52 for(i = p; i < slen; i++) {
53 sum = sum*10 + s[i]-‘0‘;
54 if(sum > 255) break;
55 ss[len] = ‘.‘;
56 if(s[p] == ‘0‘ && i-p > 0) break;
57 for(j = p; j <= i; j++)
58 ss[len+1+j-p] = s[j];
59 dfs2(s,cur+1,i+1,len+1+j-p);
60 }
61 }
62 void go(int index) {
63 char s[60];
64 int i,j,len;
65 strcpy(s,temp[index]);
66 len = strlen(temp[index]);
67 for(i = len-1,j = len; i >= 0; i--,j++)
68 s[j] = s[i];
69 s[j] = ‘\0‘;
70 dfs2(s,0,0,0);
71 for(i = len-2,j = len; i >= 0; i--,j++)
72 s[j] = s[i];
73 s[j] = ‘\0‘;
74 dfs2(s,0,0,0);
75 }
76 int main() {
77 int i;
78 while(~scanf("%d",&n)) {
79 for(i = 0; i < n; i++)
80 scanf("%d",bit+i);
81 tot = cnt = 0;
82 memset(vis,false,sizeof(vis));
83 for(i = 2; i <= 6; i++) dfs(0,i,0);
84 for(i = 0; i < cnt; i++) go(i);
85 printf("%d\n",tot);
86 for(i = 0; i < tot; i++)
87 printf("%s\n",ans[i]);
88 }
89 return 0;
90 }
xtu summer individual-4 A - Beautiful IP Addresses