LeetCode - Isomorphic Strings

Isomorphic Strings

2015.4.30 15:54

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.

Solution:

　　Think about the string pair "abb" and "cdd". An isomorphic pair is like one-to-one mapping. So we use the basic priniciple: injective + surjective = bijective.

　　Check if the mapping from s to t is onto, and t to s as well. If both hold, they're isomorphic.

Accepted code:

#include <cstring>
using namespace std;

class Solution {
public:
    bool isIsomorphic(string s, string t) {
        return check(s, t) && check(t, s);
    }
private:
    bool check(string s, string t) {
        char a[256];
        
        memset(a, 0, sizeof(a));
        int i;
        int n = s.length();
        
        for (i = 0; i < n; ++i) {
            if (a[s[i]] == 0) {
                a[s[i]] = t[i];
            }
            s[i] = a[s[i]];
        }
        
        return s == t;
    }
};