[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)

Hide Tags

Backtracking String

思路：dfs，backtrace，ip只能由3位数字组成，1、2、3位逐一尝试， 2位的时候第一位不能为0,3位是0~255

class Solution {
vector<string> m_res;
vector<string> m_str;
public:
void dfs(int dep, string s)
{
//printVector(m_str);
if(m_str.size() > 4)
return;
if(m_str.size() == 4 && dep < s.size())
return;

if(dep == s.size())
{
if(m_str.size() == 4)
{
string tmpStr;
for(int i = 0; i < 3; i++)
{
tmpStr += (m_str[i] + ".");
}
tmpStr += m_str[3];
m_res.push_back(tmpStr);
}
return;
}

for(int i = 1; i <= 3; i++)
{
if((dep+i-1) >= s.size())
break;
if(i == 2)
{
if(s[dep] == '0')
break;
}
else if(i == 3)
{
if(s[dep] == '1' ||
(s[dep] == '2' && (s[dep+1] <= '4' || (s[dep+1] == '5' && s[dep+2] < '6'))))
;
else
break;
}
m_str.push_back(s.substr(dep, i));
dfs(dep + i, s);
m_str.pop_back();
}

}
vector<string> restoreIpAddresses(string s)
{
m_res.clear();
m_str.clear();
dfs(0, s);
return m_res;
}
};