87. Scramble String

class Solution {
public:
    bool isScramble(string s1, string s2) {
        if(s1==s2)
            return true;
        if(s1.size()!=s2.size())return false;
        map<char,int> count;
        for(int i=0;i<s1.size();i++)
        {
            count[s1[i]]++;
            count[s2[i]]--;
        }
        for(map<char,int>::iterator it=count.begin();it!=count.end();it++)
            if(it->second!=0)
                return false;
        for(int i=1;i<s1.size();i++)
        {
            if(isScramble(s1.substr(0,i),s2.substr(0,i))&&isScramble(s1.substr(i),s2.substr(i)))
                return true;
            if(isScramble(s1.substr(0,i),s2.substr(s2.size()-i))&&isScramble(s1.substr(i),s2.substr(0,s2.size()-i)))
                return true;
        }
        return false;
    }

增加cache 用来记忆s1和s2是否scramble

class Solution {
private:
    map<string,bool> cache;
public:
    bool isScramble(string s1, string s2) {
        if(s1==s2)
            return true;
        if(cache.count(s1+s2))return cache[s1+s2];//在cache中查找是否已经存储了s1和s2的情况
        if(s1.size()!=s2.size())return false;
        map<char,int> count;
        for(int i=0;i<s1.size();i++)
        {
            count[s1[i]]++;
            count[s2[i]]--;
        }
        for(map<char,int>::iterator it=count.begin();it!=count.end();it++)
            if(it->second!=0)
            {
                cache[s1+s2]=false;
                return false;
            }
        for(int i=1;i<s1.size()&&!cache[s1+s2];i++)
        {
            if(isScramble(s1.substr(0,i),s2.substr(0,i))&&isScramble(s1.substr(i),s2.substr(i)))
            {
                cache[s1+s2]=true;
                return true;
            }
            if(isScramble(s1.substr(0,i),s2.substr(s2.size()-i))&&isScramble(s1.substr(i),s2.substr(0,s2.size()-i)))
            {
                cache[s1+s2]=true;
                return true;
            }
        }
        cache[s1+s2]=false;
        return false;
    }