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

 1 class Solution {
 2 public:
 3     void dfs(vector<string> &ret, string tmp, string s, int dep, int maxsize, int beg) {
 4         if (beg > maxsize) return;
 5         if (dep == 4) {
 6             if (beg == maxsize) {
 7                 tmp.erase(beg+3, 1);
 8                 ret.push_back(tmp);
 9             }
10             return;
11         }
12         dfs(ret, tmp+s[beg]+'.',s, dep+1, maxsize, beg+1);
13         if (s.substr(beg, 2) >= "10" && s.substr(beg, 2) <= "99")
14             dfs(ret, tmp+s.substr(beg, 2)+'.', s, dep+1, maxsize, beg+2);
15         if (s.substr(beg, 3) >= "100" && s.substr(beg, 3) <= "255")
16             dfs(ret, tmp+s.substr(beg, 3)+'.', s, dep+1, maxsize, beg+3);
17     }
18     vector<string> restoreIpAddresses(string s) {
19         // Start typing your C/C++ solution below
20         // DO NOT write int main() function
21         vector<string> ret;
22         string tmp = "";
23         dfs(ret, tmp, s, 0, s.size(), 0);
24         return ret;
25     }
26 };

 1 public class Solution {
 2     public List<string> RestoreIpAddresses(string s) {
 3         List<string> ans = new List<string>();
 4         string tmp = "";
 5         dfs(ref ans, tmp, s, 0, s.Length, 0);
 6         return ans;
 7     }
 8     public void dfs(ref List<string> ans, string tmp, string s, int dep, int maxSize, int beg) {
 9         if (beg > maxSize) return;
10         if (dep == 4) {
11             if (beg == maxSize) {
12                 ans.Add(tmp.Substring(0, tmp.Length-1));
13             }
14             return;
15         }
16         if (beg < maxSize) dfs(ref ans, tmp + s[beg] + '.', s, dep + 1, maxSize, beg + 1);
17         if (beg + 2 <= maxSize && string.Compare(s.Substring(beg, 2), "10") >= 0 && string.Compare(s.Substring(beg, 2), "99") <= 0) 
18             dfs(ref ans, tmp + s.Substring(beg, 2) + '.', s, dep + 1, maxSize, beg + 2);
19         if (beg + 3 <= maxSize && string.Compare(s.Substring(beg, 3), "100") >= 0 && string.Compare(s.Substring(beg, 3), "255") <= 0)
20             dfs(ref ans, tmp + s.Substring(beg, 3) + '.', s, dep + 1, maxSize, beg + 3);
21     }
22 }

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