Restore IP Addresses

来源：互联网发布：毒狗药三步倒淘宝编辑：程序博客网时间：2024/04/29 17:02

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)

思路：DFS思路， IP address的特点是一定是四段，每段数字的大小介于0-255之间（除第一段不能为0外）。题中有两个限制，一个是通过count来控制剩余的位数；另一个是start开始判断是否每个段数的大小<256。

class Solution {public:    vector<string> restoreIpAddresses(string s) {        vector<string> result;        if (s.size() < 4 || s.size() > 12) {            return result;        }                restoreUtil(s, result, "", 0, 0);        return result;    }        void restoreUtil(string s, vector<string> &result, string temp, int start, int count) {                if (count == 4 && start == s.size()) {            temp.pop_back();            result.push_back(temp);            return;        }                //通过剩余的位数来判断是否合法        int remains = s.size() - start;          if (remains < 4 - count || remains > (4 - count) * 3) {              return;          }                  int address = 0;        for (int i = 0; i < 3 && i + start < s.size(); i++) {            address = address * 10 + s[start+i] - '0';            if (address < 256) {                restoreUtil(s, result, temp + s.substr(start, i + 1) + '.', start + i + 1, count + 1);            }                        if (address == 0) {                break;            }        }    }};

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