[LeetCode] 205. Isomorphic Strings 同構字符串

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 = t = 
Output: true
"egg","add"

Example 2:

Input: s = t = 
Output: false"foo","bar"

Example 3:

Input: s = t = 
Output: true"paper","title"

Note:
You may assume both s and t have the same length.

給定兩個字符串s和t，判斷它們是不是同構的。若是字符串s能夠經過字符替換的方式獲得字符串t，則稱s和t是同構的。字符的每一次出現都必須被其對應字符所替換，同時還須要保證原始順序不發生改變。兩個字符不能映射到同一個字符，可是字符能夠映射到其自己。假設兩個字符串長度相等。 

解法1: 將字符串所有輸出成數字序列， Given "paper", return "01023". Given "isomorphic", return "0123245607". 最後在比較兩個數字是否相等。超時不能Accept。

解法2: 哈希表，用哈希表記錄每個字符出現的位置，若是對應的字符出現的位置不同，就返回False，到最後都同樣就返回True。也能夠只記錄最後一個字符出現的位置，由於以前出現的位置已經比較過了。

Java:

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;
    }
}　　

Java:

class Solution {
    public boolean isIsomorphic(String s, String t) {
        int[] a = new int[256];
        int[] b = new int[256];
        for (int i = 0; i < 256; i++) {
            a[i] = b[i] = -1;
        }
        int len = s.length();
        for (int i = 0; i < len; i++) {
            if (a[s.charAt(i)] != b[t.charAt(i)]) {
                return false;
            }
            a[s.charAt(i)] = b[t.charAt(i)] = i;
        }
        
        return true;                 
    }
}　　

Python: wo

class Solution(object):
    def isIsomorphic(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """       
        ms, mt = {}, {}
        for i in xrange(len(s)):
            if ms.get(s[i]) != mt.get(t[i]):
                return False
            ms[s[i]] = i
            mt[t[i]] = i
            
        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;
    }
};

　　

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