ip地址的恢复

给一个由数字组成的字符串。求出其可能恢复为的所有IP地址。

样例

给出字符串 "25525511135"，所有可能的IP地址为：

[
  "255.255.11.135",
  "255.255.111.35"
]

（顺序无关紧要）

class Solution {
public vector<string> restoreIpAddresses(string& s) {
        // Write your code here
        int n = s.length();
	    vector<string> buf;
	    vector<string> result;
	    visit(s, 1, 0, n, buf, result);
	    
	    return result;
    }
private void visit(string &s, int index, int begin, int n, vector<string> &buf, vector<string> &result)
    {
	    if (begin >= n || index > 4)
	    {
		    return;
	    }

	    if (index == 4)
	    {
		    if (n-begin > 3)
		    {
			    return;
		    }
		    string temp = s.substr(begin);
		    if (n-begin < 3 || temp <= "255")
		    {
		        if ((n-begin) > 1 && s[begin] == '0')
		        {
		            return;
		        }
			    buf.push_back(temp);
			    string a;
			    for (int i = 0; i < 3; i++)
			    {
				    a += buf[i] + ".";
			    }
			    a += buf[3];
			    result.push_back(a);
			    buf.pop_back();
		    }

		    return;
	    }

	    for (int len = 1; len <= 3; len++)
	    {
		    if (len == 1)
		    {
			    buf.push_back(s.substr(begin, len));
			    visit(s, index+1, begin+len, n, buf, result);
			    buf.pop_back();
		    }
		    else if (len == 2)
		    {
		        if (s[begin] == '0')
		        {
		            continue;
		        }
		        else
		        {
		            string temp = s.substr(begin, 2);
		            buf.push_back(temp);
		            visit(s, index+1, begin+len, n, buf, result);
		            buf.pop_back();
		        }
		    }
		    else 
		    {
		        if (s[begin] == '0')
		        {
		            continue;
		        }
		        else
		        {
			        string temp = s.substr(begin, 3);
			        if (temp <= "255")
			        {
				        buf.push_back(temp);
				        visit(s, index+1, begin+len, n, buf, result);
				        buf.pop_back();
			        }
		        }
		    }
	    }
    }
};