205. Isomorphic Strings | 判断两个字符串形式是否相同

Given two strings s and t, determine if they are isomorphic.

Two strings are isomorphic if the characters in s can be replaced to get t.

All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.

For example,

Given 

"egg"

, 

"add"

,
return true.

Given 

"foo"

, 

"bar"

,
return false.

Given 

"paper"

, 

"title"

,
return true.

Note:

You may assume both s and t have the same length.

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思路:用两个hash数组，分别记录s和t的字符的下一个相同的位置，如果没有下一个相同的，则是当前位置，创造hash数组时从后往前遍历两个字符串的字符。
public class Solution {
public boolean isIsomorphic(String s, String t) {
if (s.length() == 0) {
return true;
}
int hashs[] = new int[256];
int hasht[] = new int[256];
int len = s.length();
int hashnexts[] = new int[s.length()];
int hashnextt[] = new int[t.length()];

hashnexts[len - 1] = hashnextt[len - 1] = len - 1;

for (int i = len - 1; i >= 0; i--) {
if (hashs[s.charAt(i)] > 0) {
hashnexts[i] = hashs[s.charAt(i)];
}
if (hasht[t.charAt(i)] > 0) {
hashnextt[i] = hasht[t.charAt(i)];
}
hashs[s.charAt(i)] = i;
hasht[t.charAt(i)] = i;
}

for (int j = 0; j < len; j++) {
if (hashnexts[j] != hashnextt[j]) {
return false;
}
}

return true;
}
}