Method isPart

93. Restore IP Addresses/Solution.cpp:12–16

class Solution {
public:
    bool isPart(string str) {
        if (str.size() > 3 or str.size() == 0) return false;
        int i = stoi(str);
        return i <= 255 and 0 <= i and (i == 0 ? str.size() == 1 : str[0] != '0');
    }

    vector<string> ipFromNPart(int n, string str) {
        vector<string> res ;