Java 3ms beats 99.25%

  • 22

    Since all the test cases use ASCII characters, you can use small arrays as a lookup tables.

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

  • 5

    great solution, so it uses the arrays to minic two hash table, but more efficient than hash table.

  • 0

    can someone explain me this solution???

  • 0

    if(sm[sc] == 0 && tm[tc] == 0)

    Is it actually correct to compare with 0 here? 0 can also be a valid char(first char), right?

  • 0

    @eric108 The array sm[] and tm[] is the hash map. if sm[sc] == 0, then there is no key sc in the map. Since when you create the array sm[],the value is assigned to 0. With sm[sc] = tc, we say that sc is the key and tc is the value.

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