递归和回溯_leetcode93-经典的回溯题

class Solution(object):
    def restoreIpAddresses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        self.res = []

        self.findCombination(s,"",0)
        return self.res


    def findCombination(self,s,ans,count):


        if not s:
            return 


        if count == 3:

            curNum = int(s)
            if curNum >= 0 and curNum < 256:
                ans = ans + "." + s
                print ans
                self.res.append(ans)
                return



        length = len(s)
        for i in range(1,length+1):


            strNum = s[0:i]
            curNum = int(strNum)

            if curNum >= 0 and curNum < 256:

                if count == 0:

                    oldAns = ans
                    ans = ans + strNum
                    self.findCombination(s[i:],ans,count+1)
                    ans = oldAns


                else:
                    oldAns = ans
                    ans = ans + "." + strNum
                    self.findCombination(s[i:],ans,count+1)
                    ans = oldAns

            else:
                break





class Solution2(object):
    def restoreIpAddresses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        self.res = []

        self.findCombination(s,"",0)
        return self.res


    def findCombination(self,s,ans,count):


        if not s  or  len(s) > 12:
            return


        if count == 3:



            curNum = int(s)

            if len(s) >1 and int(s[0]) == 0:
                return

            if curNum >= 0 and curNum < 256:
                ans = ans + "." + s
                print ans
                self.res.append(ans)
                return



        length = len(s)
        for i in range(1,length+1):


            strNum = s[0:i]
            curNum = int(strNum)

            if len(strNum) > 1 and int(strNum[0]) == 0:
                return

            if curNum >= 0 and curNum < 256:

                if count == 0:

                    oldAns = ans
                    ans = ans + strNum
                    self.findCombination(s[i:],ans,count+1)
                    ans = oldAns


                else:
                    oldAns = ans
                    ans = ans + "." + strNum
                    self.findCombination(s[i:],ans,count+1)
                    ans = oldAns

            else:
                break



s = Solution2()

ip = "1111"

s.restoreIpAddresses(ip)

print s.res