Scramble String

Given a string s1, we may represent it as a binary tree by partitioning it to two non-empty substrings recursively.

Below is one possible representation of s1 = "great":

    great   /      gr    eat / \    /  g   r  e   at           /           a   t

To scramble the string, we may choose any non-leaf node and swap its two children.

For example, if we choose the node "gr" and swap its two children, it produces a scrambled string "rgeat".

    rgeat   /      rg    eat / \    /  r   g  e   at           /           a   t

We say that "rgeat" is a scrambled string of "great".

Similarly, if we continue to swap the children of nodes "eat" and "at", it produces a scrambled string "rgtae".

    rgtae   /      rg    tae / \    /  r   g  ta  e       /       t   a

We say that "rgtae" is a scrambled string of "great".

Given two strings s1 and s2 of the same length, determine if s2 is a scrambled string of s1.

递归来做，也就是s1分为s11和s12，s2分为s21和s22。

判断isScramble(s11,s21)&&isScramble(s12,s22)或者isScramble(s12,s21)&&isScramble(s11,s22)

base case是字符串相同

另外在进入递归前需要剪枝，判断两个字符串是否包含相同的字母，O(n)复杂度。参考http://blog.csdn.net/doc_sgl/article/details/12401335

class Solution {public:    bool isScramble(string s1, string s2) {        //base case        if(s1 == s2)            return true;        //to here, s1 != s2                //check permutation        vector<int> Dict(26,0); //a~z                for(int i = 0; i < s1.size(); i ++)            Dict[s1[i]-‘a‘] ++;        for(int i = 0; i < s2.size(); i ++)            Dict[s2[i]-‘a‘] --;        for(int i = 0; i < Dict.size(); i ++)            if(Dict[i] != 0)                return false;        //to here, s1 and s2 must have same size        int size = s1.size();                //recursion        for(int i = 1; i < size; i ++)        {            if((isScramble(s1.substr(0, i), s2.substr(0, i))&&isScramble(s1.substr(i), s2.substr(i)))             ||(isScramble(s1.substr(0, i), s2.substr(size-i))&&isScramble(s1.substr(i), s2.substr(0, size-i))))                return true;        }        return false;    }};

【LeetCode】Scramble String