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LeetCode: Restore IP Addresses
Given a string containing only digits, restore it by returning all possible valid IP address combinations.
For example:
Given "25525511135",
return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)
地址：https://oj.leetcode.com/problems/restore-ip-addresses/
算法：递归构造。一个ip地址有四个数字，每个数字必须在0到255之间，并且不能第一个非零数字不能以零开头。基本的思想是，取最后一个数字，看其是否合理，如果合理在递归构造前面三个数字；取最后两个数字，如果合理在递归前面三个数字；取最后三个数字，如果合理在递归构造前面三个数字。代码：
1 class Solution {
2 public:
3 vector<string> restoreIpAddresses(string s) {
4 vector<string> result;
5 partitionIpAddresses(s,4,result);
6 return result;
7 }
8 bool partitionIpAddresses(string s, int n, vector<string> &result){
9 if(n <= 0 || s.empty()){
10 return false;
11 }
12 if(n == 1){
13 int val = atoi(s.c_str());
14 if(val < 256 && isValidataion(s)){
15 result.push_back(s);
16 return true;
17 }else{
18 return false;
19 }
20 }
21 int i = s.size() - 1;
22 int val = atoi(s.substr(i,1).c_str());
23 vector<string> temp;
24 bool flag = partitionIpAddresses(s.substr(0,s.size()-1), n-1, temp);
25 if(flag){
26 for(int j = 0; j < temp.size(); ++j){
27 if(isValidataion(s.substr(i,1)))
28 result.push_back(temp[j] + "." + s.substr(i,1));
29 }
30 }
31 temp.clear();
32 --i;
33 if(i >= 0){
34 val = atoi(s.substr(i,2).c_str());
35 flag = partitionIpAddresses(s.substr(0,s.size()-2), n-1, temp);
36 if(flag){
37 for(int j = 0; j < temp.size(); ++j){
38 if(isValidataion(s.substr(i,2)))
39 result.push_back(temp[j] + "." + s.substr(i,2));
40 }
41 }
42 }
43 temp.clear();
44 --i;
45 if(i >= 0){
46 val = atoi(s.substr(i,3).c_str());
47 if(val < 256){
48 flag = partitionIpAddresses(s.substr(0,s.size()-3), n-1, temp);
49 if(flag){
50 for(int j = 0; j < temp.size(); ++j){
51 if(isValidataion(s.substr(i,3)))
52 result.push_back(temp[j] + "." + s.substr(i,3));
53 }
54 }
55 }
56 }
57 return !result.empty();
58 }
59 bool isValidataion(const string &s){
60 if(s.size() < 1) return false;
61 if(s.size() == 1) return true;
62 if(s[0] == ‘0‘) return false;
63 return true;
64 }
65 };
LeetCode: Restore IP Addresses
标签：style blog http color os io strong ar for
原文地址：http://www.cnblogs.com/boostable/p/leetcode_restore_ip_addresses.html
