leetcode 日经贴，Cpp code -Restore IP Addresses

class Solution {
public:
void gen(const string &s, int pos, int k, vector<string> &ips, string &curstring) {
int n = s.length();
if (k == 4) {
if (n == pos) {
ips.push_back(curstring);
}
return ;
}
int v = 0;
for (int i = pos; i < min(pos + 3, n); ++i) {
v = v * 10 + int(s[i] - '0');
if (v <= 255 && n - i - 1 >= 3 - k && (i - pos == 0 || s[pos] > '0')) {
string nip = curstring;
if (k > 0) {
nip += '.';
}
nip += s.substr(pos, i - pos + 1);
gen(s, i + 1, k + 1, ips, nip);
}
}
}
vector<string> restoreIpAddresses(string s) {
vector<string> ret;
string ip;
gen(s, 0, 0, ret, ip);
return ret;
}
};