[LeetCode] Restore IP Addresses

最新推荐文章于 2019-05-24 09:26:32 发布

原创最新推荐文章于 2019-05-24 09:26:32 发布 · 285 阅读

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本文详细阐述了如何通过递归深度优先搜索算法，从给定的数字字符串中生成所有可能的有效IP地址组合。

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)

class Solution {
public:
    vector<string> ans;
    int pos[4];
    vector<string> restoreIpAddresses(string s) {
        dfs(0,4,s,0);
        return ans;
    }
    void dfs(int dep,int maxDep,string s,int start){
        if(dep == maxDep){
            if(start == s.size()){
                int beg = 0;
                string addr;
                for(int i = 0;i < maxDep;i ++){
                    string ip(s,beg,pos[i] - beg + 1);
                    addr += i == 0 ? ip : "." + ip;
                    beg = pos[i] + 1;
                }
                ans.push_back(addr);
            }
            return;
        }
        for(int i = start;i < s.size();i ++){
            string num(s,start,i - start + 1);
            if(check(num)){
                pos[dep] = i;
                dfs(dep + 1,maxDep,s,i + 1);
            }
        }
    }
    bool check(string num){
        if(num.length()==1 && num>="0" && num<="9")return true;
        if(num.length()==2 && num>="10" && num<="99")return true;
        if(num.length()==3 && num>="100" && num<="255")return true;
        return false;
    }
};