Python3解leetcode Isomorphic Strings

问题描述：

 

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.

 

思路：

两个字符串对应位置上的字母要具有一一对应的关系，即假如s[1]=s,t[1]=t,则s对应的就是t,如果后面s[i]=s,则t[i]也必须为 t，若t[i]为其他字母，则判定为非同形态。

这种一一对应关系，首先考虑字典

代码：

 

class Solution:
    def isIsomorphic(self, s: str, t: str) -> bool:
        table = dict()
        for i in range(len(s)):
            if s[i] not in table:
                table[s[i]] = t[i]
            elif table[s[i]] != t[i]:
                return False
        return len(table) == len(set(table.values()))

 

如果字典中没有相应键值对，那么就在字典中加入该键值对；如果有该键值对，判断一下该元素是否和原存储的键值对相同，不相同则肯定是非同形态，如果相同则是到目前为止为同形态。

有一种特殊情况，就是不同的键，对应了相同的值，如s='ab',t=‘aa’，出现这种情况代表是非同形态的，通过判断键、值的个数来判断是否出现这种情况。