# Strings Homomorphism

## Question

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.

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

Example
Given s = “egg”, t = “add”, return true.
Given s = “foo”, t = “bar”, return false.
Given s = “paper”, t = “title”, return true.

## Thinking

• same length (not null)
• one array save charactor’s int value
• another array save charactor’s postions in the string
• check each charactor’s postion values

## Java

``````public class Solution {
/**
* @param s a string
* @param t a string
* @return true if the characters in s can be replaced to get t or false
*/
public boolean isIsomorphic(String s, String t) {
// Write your code here
if (s == null || t == null) {
return false;
}
if (s.length() != t.length()) {
return false;
}
// char value as postions, point to PosValue array
int[] sPos = new int[s.length()];
int[] tPos = new int[s.length()];
// count of char valuess
int[] sPosValue = new int[128];
int[] tPosValue = new int[128];
for (int i = 0; i < s.length(); i++) {
int sIndex = (int) s.charAt(i);
int tIndex = (int) t.charAt(i);
sPos[i] = sIndex;
tPos[i] = tIndex;
sPosValue[sIndex] = sPosValue[sIndex] * 10 * i + 1;
tPosValue[tIndex] = tPosValue[tIndex] * 10 * i + 1;
}
for (int i = 0; i < sPos.length; i++) {
if (sPosValue[sPos[i]] != tPosValue[tPos[i]]) {
return false;
}
}
return true;
}
}
``````