String Programs

IsomorphicStrings.java

// Java program to check if two strings
// areIsomorphic
 
import java.io.*;
import java.util.*;
 
class GFG {
 
    static boolean areIsomorphic(String str1, String str2)
    {
 
        HashMap<Character, Character> charCount
            = new HashMap();
        char c = 'a';
        for (int i = 0; i < str1.length(); i++) {
            if (charCount.containsKey(str1.charAt(i))) {
                c = charCount.get(str1.charAt(i));
                if (c != str2.charAt(i))
                    return false;
            }
            else if (!charCount.containsValue(
                         str2.charAt(i))) {
                charCount.put(str1.charAt(i),
                              str2.charAt(i));
            }
            else {
                return false;
            }
        }
        return true;
    }
 
    /* Driver code*/
    public static void main(String[] args)
    {
 
        String str1 = "aac";
        String str2 = "xxy";
 
        // Function Call
        if (str1.length() == str2.length()
            && areIsomorphic(str1, str2))
            System.out.println("True");
        else
            System.out.println("False");
    }
}

LongestStringWithoutRepeats.java

class Solution {


    public int lengthOfLongestSubstring(String s) {
        Map<Character, Integer> chars = new HashMap();

        int left = 0;
        int right = 0;

        int res = 0;

        // sliding window
        // |---|-------|---|
        //     left    right

        while(right < s.length()) {
            char current = s.charAt(right);

            // keep incrementing count right pointer character
            chars.put(current, chars.getOrDefault(current, 0) + 1);

            while(chars.get(current) > 1) {
                // repeat detected
                // shorten window until no repeats
                char back = s.charAt(left);
                chars.put(back, chars.get(back) -1);
                left ++;
            }

            res = Math.max(right-left+1, res);

            right++;
        }

        return res;
    }
}

ParanthesisGenerator.java

class Solution {
    public List<String> generateParenthesis(int n) {
        List<String> ans = new ArrayList();
        if (n == 0) {
            ans.add("");
        } else {
            for (int c = 0; c < n; ++c)
                for (String left: generateParenthesis(c))
                    for (String right: generateParenthesis(n-1-c))
                        ans.add("(" + left + ")" + right);
        }
        return ans;
    }
}

RomanNumerals.java

class Solution {
    static Map<Character, Integer> map = new HashMap<>();

    static {
        map.put('I', 1);
        map.put('V', 5);
        map.put('X', 10);
        map.put('L', 50);
        map.put('C', 100);
        map.put('D', 500);
        map.put('M', 1000);
    }

    public int romanToInt(String s) {

        int i = 0;

        int sum = 0;

        while(i<s.length() - 1) {
            if(map.get(s.charAt(i)) < map.get(s.charAt(i + 1))) {
                sum += map.get(s.charAt(i+1)) - map.get(s.charAt(i));
                i += 2;
            }
            else {
                sum += map.get(s.charAt(i));
                i += 1;
            }
        }

        if(i == s.length() - 1) {
            sum += map.get(s.charAt(i));
        }

        return sum;
    }
}

ShortestDistanceBetweenWords.java

// Java code to implement the approach

import java.io.*;

class GFG {
    
// Function to return shortest distance
static int shortestDistance(String[] s,
                    String word1, String word2)
{
    int d1 = -1, d2 = -1;
    int ans = Integer.MAX_VALUE;

    // Traverse the string
    for (int i = 0; i < s.length; i++) {
        if (s[i] == word1)
            d1 = i;
        if (s[i] == word2)
            d2 = i;
        if (d1 != -1 && d2 != -1)
            ans = Math.min(ans, Math.abs(d1 - d2));
    }

    // Return the answer
    return ans;
}

 // Driver Code
    public static void main (String[] args) {
        String[] S
        = { "the", "quick", "brown", "fox", "quick" };

    String word1 = "the", word2 = "fox";

    // Function Call
    System.out.println(shortestDistance(S, word1, word2));
    }
}