leetcode 205: Isomorphic Strings

題目描述：

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.

解題思路

使用兩個char數組sm,st sm[s[i]] = t[i]; st[t[i]] = s[i];

public class Solution {
    public boolean isIsomorphic(String s, String t) {
    if(s==null || t==null)
        return false;
    if(s.length()!=t.length())
        return false;
    char[] sa = s.toCharArray();
    char[] ta = t.toCharArray();
    char[] sm = new char[256];
    char[] tm = new char[256];
    for(int i = 0 ; i<sa.length;i++){
        char sc = sa[i];
        char tc = ta[i];
        if(sm[sc] == 0 && tm[tc]==0){
            sm[sc] = tc;
            tm[tc] = sc;
        }else{
            if(sm[sc]!=tc || tm[tc]!=sc){
                return false;
            }
        }
    }
    return true;
}
}