[LintCode/LeetCode] Scramble String

MASAILA 发布于2019-08-14 15:45 / 3449人阅读

摘要：首先将两个字符串化成字符数组，排序后逐位比较，确定它们等长且具有相同数量的相同字符。然后，从第一个字符开始向后遍历，判断和中以这个坐标为中点的左右两个子字符串是否满足第一步中互为的条件设分为和，分为和。

Problem

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.

Challenge

O(n3) time

Note

首先将两个字符串化成字符数组，排序后逐位比较，确定它们等长且具有相同数量的相同字符。
然后，从第一个字符开始向后遍历，判断s1和s2中以这个坐标为中点的左右两个子字符串是否满足第一步中互为scramble string的条件：
设s1分为a1和b1，s2分为a2和b2。若a1和a2满足且b1和b2满足（令a1和a2长度相等，b1和b2长度相等），或a1和b2满足且a2和b1满足（令a1和b2长度相等，a2和b1长度相等），就break出来，返回true；
若遍历完s1，仍旧没有满足条件的情况，返回false。

Solution

public class Solution {
    public boolean isScramble(String s1, String s2) {
        if (s1.equals(s2)) return true;
        char[] sc1 = s1.toCharArray();
        char[] sc2 = s2.toCharArray();
        Arrays.sort(sc1);
        Arrays.sort(sc2);
        for (int i = 0; i < sc1.length; i++) {
            if (sc1[i] != sc2[i]) return false;
        }
        int mid = 1;
        boolean res = false;
        while (mid < s1.length()) {
            res = (isScramble(s1.substring(0, mid), s2.substring(0, mid)) && 
                    isScramble(s1.substring(mid, s1.length()), s2.substring(mid, s2.length())))
                    ||  (isScramble(s1.substring(0, mid), s2.substring(s2.length()-mid, s2.length())) && 
                    isScramble(s1.substring(mid, s1.length()), s2.substring(0, s2.length()-mid)));
            if (res) break;
            mid++;
        }
        return res;
    }
}

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