DFS之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)

class Solution {
private:
vector<string> ret;
int pos[4];
public:
bool check(string &s, int beg, int end)
{
string ip(s, beg, end - beg + 1);
if (ip.size() == 1)
return "0" <= ip && ip <= "9";
else if (ip.size() == 2)
return "10" <= ip && ip <= "99";
else if (ip.size() == 3)
return "100" <= ip && ip <= "255";
else
return false;
}

void dfs(int dep, int maxDep, string &s, int start)
{
if (dep == maxDep)
{
if (start == s.size())
{
int beg = 0;
string addr;
for(int i = 0; i < maxDep; i++)
{
string ip(s, beg, pos[i] - beg + 1);
beg = pos[i] + 1;
addr += i == 0 ? ip : "." + ip;
}
ret.push_back(addr);
}
return;
}

for(int i = start; i < s.size(); i++)
if (check(s, start, i))
{
pos[dep] = i;
dfs(dep + 1, maxDep, s, i + 1);
}
}

vector<string> restoreIpAddresses(string s) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
ret.clear();
dfs(0, 4, s, 0);
return ret;
}
};