算法精粹(algorithm-essentials)

感谢soulmachine@github提供内容
## Isomorphic Strings

### 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.

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.


### 分析

用两个HashMap维护字符的映射关系,时间复杂度`O(n)`,空间复杂度`O(n)`。


### 代码

{% if book.java %}
```java
// Isomorphic Strings
// Time Complexity: O(n), Space Complexity: O(n)
public class Solution {
public boolean isIsomorphic(String s, String t) {
if (s.length() != t.length()) return false;

final Map map1 = new HashMap<>();
final Map map2 = new HashMap<>();

for (int i = 0; i < s.length(); ++i) {
final char c1 = s.charAt(i);
final char c2 = t.charAt(i);

if (map1.containsKey(c1)) {
if (map1.get(c1) != c2) return false;
} else {
map1.put(c1, c2);
}

if (map2.containsKey(c2)) {
if (map2.get(c2) != c1) return false;
} else {
map2.put(c2, c1);
}
}
return true;
}
}
```
{% endif %}


### 相关题目

* [Word Pattern](word-pattern.md)