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# # 205. Isomorphic Strings

[LeetCode](https://leetcode.com/problems/isomorphic-strings/)

```
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.

input: 兩個 string
output: 找出是否對應
```

```
xample 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

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isIsomorphic = function(s, t) {}
```

### Edge Case

* s = "ab",  t="aa"
* s="aa",  t="ab"

### 如何解

一開始用 map 解，後來發現有一個限制是 以下，所以除了 key 是唯一，連 value 也要是唯一

```
No two characters may map to the same character
```

### Code

```
var isIsomorphic = function(s, t) {
 let lookupS = {};
   let lookupT = {}
   for(let i = 0; i< s.length; i++){
    // didn't have this key before then add
    if(!lookupS[s[i]] && !lookupT[t[i]]){
      lookupS[s[i]] = t[i];
      lookupT[t[i]] = s[i];
    }else{
      if(lookupS[s[i]] !== t[i]){
        return false
      }
    }
   }
    return true;
};
```