[leetcode]Scramble String

题不难，但是开始没理解意思

用DFS就过了

枚举从哪儿断开的

有两种情况

1、正常的

2、交换了的

result = isScramble(s1.substr(0,i) , s2.substr(0,i)) && isScramble(s1.substr(i) , s2.substr(i));

这是正常的比较

result = isScramble(s1.substr(0,i) , s2.substr(s1.size()-i,i)) && isScramble(s1.substr(i) , s2.substr(0 , s1.size()-i));

这是交换了的比较

class Solution {
public:
    bool isScramble(string s1, string s2) {
        //first count the characters
        if(s1 == s2) return true;
        if(s1.size() != s2.size()) return false;
        int charset[26] = {0};
        for(int i = 0 ; i < s1.size() ; ++i)
          charset[s1[i]-'a']++;
        for(int i = 0 ; i < s2.size() ; ++i)
          charset[s2[i]-'a']--;
        for(int i = 0 ; i < 26 ; ++i)
          if(charset[i] != 0) return false;
        //end
        
        bool result = false;
        for(int i = 1 ; i < s1.size() ; ++i) {
            result = isScramble(s1.substr(0,i) , s2.substr(0,i)) && isScramble(s1.substr(i) , s2.substr(i));
            if(result) return true;
            result = isScramble(s1.substr(0,i) , s2.substr(s1.size()-i,i)) && isScramble(s1.substr(i) , s2.substr(0 , s1.size()-i));
            if(result) return true;
        }
        return false;
    }
};