Snapchat - IPFilter
这道题题意好难理解……
首先说一下IP，二进制表示的IP有32位，一般8位一分隔，转换成十进制，就是0.0.0.0 ~ 255.255.255.255
给你一些IP的规则，比如"7.7.7.7/8","123.2.67.3/8"，这个代表着比如7.7.7.7所对应的32位的表示，00000111*4，8表示取前8位，把所有以00000111开头的ip地址都看成一组，如果在这组内就被filter掉。
所以思路是：
1. 建立ipRule的trie，提供搜索的功能
2. 搜索
1 public List<String> filter(List<String> rules, List<String> IPs) { 2 if(rules == null || rules.size() == 0 || IPs == null || IPs.size() == 0) { 3 return IPs; 4 } 5 Trie ruleTrie = new Trie(); 6 prepareRule(ruleTrie, rules); 7 List<String> res = new ArrayList<String>(); 8 filterIPs(IPs, ruleTrie, res); 9 return res; 10 } 11 12 13 private void prepareRule(Trie ruleTrie, List<String> rules) { 14 for(String rule: rules) { 15 StringBuilder sb = new StringBuilder(); 16 String[] parts = rule.split("/"); 17 int bits = Integer.parseInt(parts[1]); 18 String[] ipBlocks = parts[0].split("\\."); 19 for(String block: ipBlocks) { 20 String blockStr = Integer.toBinaryString(Integer.parseInt(block)); 21 int leadingZeros = 8 - blockStr.length(); 22 while(leadingZeros-- > 0) { 23 sb.append("0"); 24 } 25 sb.append(blockStr); 26 } 27 String curRule = sb.toString().substring(0, bits); 28 ruleTrie.insert(curRule); 29 } 30 } 31 32 private void filterIPs(List<String> IPs, Trie ruleTrie, List<String> res) { 33 for(String ip: IPs) { 34 StringBuilder sb = new StringBuilder(); 35 String[] ipBlocks = ip.split("\\."); 36 for(String block: ipBlocks) { 37 String blockStr = Integer.toBinaryString(Integer.parseInt(block)); 38 int leadingZeros = 8 - blockStr.length(); 39 while(leadingZeros-- > 0) { 40 sb.append("0"); 41 } 42 sb.append(blockStr); 43 } 44 String binaryIP = sb.toString(); 45 if(!ruleTrie.startsWith(binaryIP)) { 46 res.add(ip); 47 } 48 } 49 } 50 51 52 class TrieNode { 53 char c; 54 boolean isLeaf; 55 TrieNode[] children; 56 57 public TrieNode() { 58 children = new TrieNode[2]; 59 isLeaf = false; 60 } 61 } 62 63 class Trie { 64 TrieNode root; 65 66 public Trie() { 67 root = new TrieNode(); 68 } 69 70 public void insert(String s) { 71 if(s == null || s.length() == 0) { 72 return; 73 } 74 TrieNode cur = root; 75 for(int i = 0; i < s.length(); i++) { 76 char c = s.charAt(i); 77 int index = c - '0'; 78 if(cur.children[index] == null) { 79 cur.children[index] = new TrieNode(); 80 } 81 cur.children[index].c = c; 82 cur = cur.children[index]; 83 } 84 cur.isLeaf = true; 85 } 86 87 public boolean startsWith(String s) { 88 TrieNode cur = root; 89 for(int i = 0; i < s.length(); i++) { 90 char c = s.charAt(i); 91 int index = c - '0'; 92 if(cur.isLeaf == true) { 93 return true; 94 } 95 if(cur.children[index] == null) { 96 return false; 97 } 98 cur = cur.children[index]; 99 } 100 return cur.isLeaf; 101 } 102 } 103 104 public static void main(String[] args) { 105 IPFilter sample = new IPFilter(); 106 List<String> rules = new ArrayList<String>(Arrays.asList("7.7.7.7/8","123.2.67.3/8")); 107 List<String> IPs = new ArrayList<String>(Arrays.asList("23.2.4.1","7.3.4.1","5.1.2.3","123.2.67.3")); 108 List<String> res = sample.filter(rules, IPs); 109 System.out.println(res); 110 }
