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Leetcode087-scrambleString

Description

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”:

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    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”.

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    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”.

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    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.

Example

Example 1:

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Input: s1 = "great", s2 = "rgeat"
Output: true

Example 2:
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Input: s1 = "abcde", s2 = "caebd"
Output: false

Solution

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class Solution {
public boolean isScramble(String s1, String s2) {
if (s1.equals(s2)) return true;

int[] test = new int[26];
for (int i = 0; i < s1.length(); i++){
test[s1.charAt(i) - 'a'] ++;
test[s2.charAt(i) - 'a'] --;
}
for (int letter: test) if (letter!=0) return false;

for (int i = 1; i < s1.length(); i++){
if (isScramble(s1.substring(0, i), s2.substring(0, i)) && isScramble(s1.substring(i), s2.substring(i))) return true;
if (isScramble(s1.substring(0, i), s2.substring(s2.length() - i)) && isScramble(s1.substring(i), s2.substring(0, s2.length() - i))) return true;
}
return false;
}
}