# 205.Isomorphic-Strings

## 题目描述

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.
Example 1:
Input: s = "egg", t = "add"
Output: true
Example 2:
Input: s = "foo", t = "bar"
Output: false
Example 3:
Input: s = "paper", t = "title"
Output: true
Note:
You may assume both s and t have the same length.

## 代码

### Approach #1

Time: O(N) && Space: O(N)
class Solution {
public boolean isIsomorphic(String s, String t) {
int[] m1 = new int[256];
int[] m2 = new int[256];
int n = s.length();
for (int i = 0; i < n; i++) {
if (m1[s[i]] != m2[t[i]]) {
return false;
}
m1[s[i]] = i + 1;
m2[t[i]] = i + 1;
}
return true;
}
}

### Approach #2 HashMap

class Solution {
public boolean isIsomorphic(String s, String t) {
if (s == null || s.length() <= 1) return true;
HashMap<Character, Character> map = new HashMap<Character, Character>();
for (int i = 0; i < s.length(); i++) {
char a = s.charAt(i);
char b = t.charAt(i);
if (map.containsKey(a)) {
if (map.get(a).equals(b)) {
continue;
} else {
return false;
}
} else {
if (!map.containsValue(b)) {
map.put(a, b);
} else {
return false;
}
}
}
return true;
}
}