Friday, August 7, 2015

LeetCode OJ - Isomorphic Strings

Problem:

Please find the problem here.

Solution:

Walk the strings together. If we haven't seen either one of the character, add it to the mapping, otherwise make sure it matches if the existing mapping or return false otherwise.

Assuming constant size alphabet, the performance is linear, which is the best possible.

Code:

#include "stdafx.h"

// https://leetcode.com/problems/isomorphic-strings/

#include "LEET_ISOMORPHIC_STRINGS.h"
#include <map>
#include <iostream>
#include <sstream>
#include <vector>
#include <string>

using namespace std;

namespace _LEET_ISOMORPHIC_STRINGS
{
    class Solution
    {
    public:
        bool isIsomorphic(string s, string t)
        {
            if (s.length() != t.length())
            {
                return false;
            }

            map<char, char> forward_map;
            map<char, char> backward_map;
            for (unsigned int i = 0; i < s.length(); i++)
            {
                map<char, char>::iterator forward_probe = forward_map.find(s[i]);
                if (forward_probe == forward_map.end())
                {
                    forward_map.insert(pair<char, char>(s[i], t[i]));
                }
                else if (forward_probe->second != t[i])
                {
                    return false;
                }

                map<char, char>::iterator backward_probe = backward_map.find(t[i]);
                if (backward_probe == backward_map.end())
                {
                    backward_map.insert(pair<char, char>(t[i], s[i]));
                }
                else if (backward_probe->second != s[i])
                {
                    return false;
                }
            }

            return true;
        }
    };
};

using namespace _LEET_ISOMORPHIC_STRINGS;

int LEET_ISOMORPHIC_STRINGS()
{
    Solution solution;
    cout << solution.isIsomorphic("egg", "add") << endl;
    cout << !solution.isIsomorphic("foo", "bar") << endl;
    cout << solution.isIsomorphic("paper", "title") << endl;
    cout << !solution.isIsomorphic("ab", "aa") << endl;
    return 0;
}

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