Problem: 2050E - Three Strings
Language: java

Solution 1 (runtime: 280 ms):
import java.util.*;

public class ThreeStrings {
    // Custom print functions
    public static void print(Object print) {
        System.out.print(print);
    }

    public static void println(Object print) {
        System.out.println(print);
    }

    public static void println() {
        System.out.println();
    }

    // Declare a 2D dp array to store memoization results
    static int[][] dp;

    // Function to compute the minimum changes required
    public static int func(int i, int j, char[] a, char[] b, char[] c) {
        int n = c.length;
        // Base case: if all characters are matched
        if (i + j >= n) return 0;

        // Check if result is already calculated
        if (dp[i][j] != -1) return dp[i][j];

        int take_a = Integer.MAX_VALUE;
        int take_b = Integer.MAX_VALUE;

        // Try taking a character from 'a'
        if (i < a.length) {
            if (a[i] == c[i + j]) {
                take_a = func(i + 1, j, a, b, c); // No change needed
            } else {
                take_a = 1 + func(i + 1, j, a, b, c); // Change needed
            }
        }

        // Try taking a character from 'b'
        if (j < b.length) {
            if (b[j] == c[i + j]) {
                take_b = func(i, j + 1, a, b, c); // No change needed
            } else {
                take_b = 1 + func(i, j + 1, a, b, c); // Change needed
            }
        }

        // Store and return the minimum changes required
        return dp[i][j] = Math.min(take_a, take_b);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt(); // Number of test cases

        for (int l = 0; l < t; l++) {
            char[] a = sc.next().toCharArray(); // Input string a
            char[] b = sc.next().toCharArray(); // Input string b
            char[] c = sc.next().toCharArray(); // Target string c

            int m = a.length;
            int n = b.length;
            int len = c.length;

            // Initialize dp array with -1
            dp = new int[m + 1][n + 1];
            for (int[] row : dp) {
                Arrays.fill(row, -1);
            }

            // Compute and print result
            println(func(0, 0, a, b, c));
        }
        sc.close();
    }
}


Solution 2 (runtime: 280 ms):
import java.util.*;

import java.lang.*;

import java.io.*;



public class Codeforces {

    public static void main(String[] args){

        FastReader fr = new FastReader();

        int tc = fr.nextInt();



        while (tc-- > 0) {

            solve(fr);

        }

    }





    private static void solve(FastReader fr) {

        String a = fr.next();

        String b = fr.next();

        String c = fr.next();

        int[][] dp = new int[a.length()+1][b.length()+1];



        for(int[] row : dp) Arrays.fill(row, -1);



        System.out.println(solve(a, b, c, 0, 0, 0, dp));

    }



    static int solve(String a, String b, String c, int i, int j, int k, int[][] dp) {

        if(k == c.length()) return 0;

        if(i > a.length() || j > b.length()) return (int)(1e7);

        boolean isAMatch = false;

        boolean isBMatch = false;



        if(dp[i][j] != -1) return dp[i][j];



        if(i < a.length() && a.charAt(i) == c.charAt(k)){

            isAMatch = true;

        }



        if(j < b.length() && b.charAt(j) == c.charAt(k)){

            isBMatch = true;

        }



        int ans1 = solve(a, b, c, i+1, j, k+1, dp) + (isAMatch ? 0 : 1);

        int ans2 = solve(a, b, c, i, j + 1, k+1, dp) + (isBMatch ? 0 : 1);



        return dp[i][j] = Math.min(ans1, ans2);

    }





    static int[] readIntArray(FastReader fr, int n){

        int[] arr = new int[n];



        for(int i = 0; i < n; i++){

            arr[i] = fr.nextInt();

        }



        return arr;

    }



    static class FastReader {

        BufferedReader br;

        StringTokenizer st;



        public FastReader() {

            br = new BufferedReader(

                    new InputStreamReader(System.in));

        }



        String next() {

            while (st == null || !st.hasMoreElements()) {

                try {

                    st = new StringTokenizer(br.readLine());

                } catch (IOException e) {

                    e.printStackTrace();

                }

            }

            return st.nextToken();

        }



        int nextInt() {

            return Integer.parseInt(next());

        }



        long nextLong() {

            return Long.parseLong(next());

        }



        double nextDouble() {

            return Double.parseDouble(next());

        }



        String nextLine() {

            String str = "";

            try {

                if (st.hasMoreTokens()) {

                    str = st.nextToken("\n");

                } else {

                    str = br.readLine();

                }

            } catch (IOException e) {

                e.printStackTrace();

            }

            return str;

        }

    }



}