Restore IP Addresses -- LeetCode - Code Ganker - 博客频道 - CSDN.NET

public ArrayList restoreIpAddresses(String s) { ArrayList res = new ArrayList(); if(s==null || s.length()==0) return res; helper(s,0,1,"",res); return res; } private void helper(String s, int index, int segment, String item, ArrayList res) { if(index>=s.length()) return; if(segment == 4) { String str = s.substring(index); if(isValid(str)) { res.add(item+"."+str); } return; } for(int i=1;i<4&&(i+index<=s.length());i++) { String str = s.substring(index, index+i); if(isValid(str)) { if(segment==1) helper(s,index+i,segment+1,str,res); else helper(s,index+i,

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