[LeetCode] 205. Isomorphic Strings 同构字符串 ll LeetCode Questions List 题目汇总

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.

给定两个字符串s和t，判断它们是否是同构的。如果字符串s可以通过字符替换的方式得到字符串t，则称s和t是同构的。字符的每一次出现都必须被其对应字符所替换，同时还需要保证原始顺序不发生改变。两个字符不能映射到同一个字符，但是字符可以映射到其本身。 

解法1: 将字符串全部输出成数字序列， Given "paper", return "01023". Given "isomorphic", return "0123245607". 最后在比较两个数字是否相等。超时不能Accept。

解法2: 哈希表，用哈希表记录每一个字符出现的位置，如果对应的字符出现的位置不一样，就返回False，到最后都一样就返回True。也可以只记录最后一个字符出现的位置，因为之前出现的位置已经比较过了。

Java:

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public class Solution {
    public boolean isIsomorphic(String s1, String s2) {
        int[] m = new int[512];
        for (int i = 0; i < s1.length(); i++) {
            if (m[s1.charAt(i)] != m[s2.charAt(i)+256]) return false;
            m[s1.charAt(i)] = m[s2.charAt(i)+256] = i+1;
        }
        return true;
    }
}　　

Python:

def isIsomorphic1(self, s, t):
    d1, d2 = {}, {}
    for i, val in enumerate(s):
        d1[val] = d1.get(val, []) + [i]
    for i, val in enumerate(t):
        d2[val] = d2.get(val, []) + [i]
    return sorted(d1.values()) == sorted(d2.values())
        
def isIsomorphic2(self, s, t):
    d1, d2 = [[] for _ in xrange(256)], [[] for _ in xrange(256)]
    for i, val in enumerate(s):
        d1[ord(val)].append(i)
    for i, val in enumerate(t):
        d2[ord(val)].append(i)
    return sorted(d1) == sorted(d2)
    
def isIsomorphic3(self, s, t):
    return len(set(zip(s, t))) == len(set(s)) == len(set(t))
    
def isIsomorphic4(self, s, t): 
    return [s.find(i) for i in s] == [t.find(j) for j in t]
    
def isIsomorphic5(self, s, t):
    return map(s.find, s) == map(t.find, t)

def isIsomorphic(self, s, t):
    d1, d2 = [0 for _ in xrange(256)], [0 for _ in xrange(256)]
    for i in xrange(len(s)):
        if d1[ord(s[i])] != d2[ord(t[i])]:
            return False
        d1[ord(s[i])] = i+1
        d2[ord(t[i])] = i+1
    return True　　

C++:

class Solution {
public:
    bool isIsomorphic(string s, string t) {
        int m1[256] = {0}, m2[256] = {0}, n = s.size();
        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;
    }
};

　　

ll LeetCode Questions List 题目汇总