LeetCode: Restore IP Addresses

erase的时候没考虑到.加上去之后删除位置的变化，基本一次过，少数次过

class Solution {
public:
    void dfs(vector<string> &ret, string tmp, string s, int dep, int maxsize, int beg) {
        if (beg > maxsize) return;
        if (dep == 4) {
            if (beg == maxsize) {
                tmp.erase(beg+3, 1);
                ret.push_back(tmp);
            }
            return;
        }
        dfs(ret, tmp+s[beg]+'.',s, dep+1, maxsize, beg+1);
        if (s.substr(beg, 2) >= "10" && s.substr(beg, 2) <= "99")
            dfs(ret, tmp+s.substr(beg, 2)+'.', s, dep+1, maxsize, beg+2);
        if (s.substr(beg, 3) >= "100" && s.substr(beg, 3) <= "255")
            dfs(ret, tmp+s.substr(beg, 3)+'.', s, dep+1, maxsize, beg+3);
    }
    vector<string> restoreIpAddresses(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<string> ret;
        string tmp = "";
        dfs(ret, tmp, s, 0, s.size(), 0);
        return ret;
    }
};

 C#

public class Solution {
    public List<string> RestoreIpAddresses(string s) {
        List<string> ans = new List<string>();
        string tmp = "";
        dfs(ref ans, tmp, s, 0, s.Length, 0);
        return ans;
    }
    public void dfs(ref List<string> ans, string tmp, string s, int dep, int maxSize, int beg) {
        if (beg > maxSize) return;
        if (dep == 4) {
            if (beg == maxSize) {
                ans.Add(tmp.Substring(0, tmp.Length-1));
            }
            return;
        }
        if (beg < maxSize) dfs(ref ans, tmp + s[beg] + '.', s, dep + 1, maxSize, beg + 1);
        if (beg + 2 <= maxSize && string.Compare(s.Substring(beg, 2), "10") >= 0 && string.Compare(s.Substring(beg, 2), "99") <= 0) 
            dfs(ref ans, tmp + s.Substring(beg, 2) + '.', s, dep + 1, maxSize, beg + 2);
        if (beg + 3 <= maxSize && string.Compare(s.Substring(beg, 3), "100") >= 0 && string.Compare(s.Substring(beg, 3), "255") <= 0)
            dfs(ref ans, tmp + s.Substring(beg, 3) + '.', s, dep + 1, maxSize, beg + 3);
    }
}