Question

Problem 1.

Write a program in Java to find the Longest Common Subsequence (LCS) using Dynamic Programming. Your program will read two strings from keyboard and display the LCS on the screen.

Assume upper and lower case letters as same.

Sample Input (taken from keyboard):

saginaw

gain

Sample output (display on the screen):

ain

Answer 1

import java.util.Scanner;

public class Main {

public static void longestCommonSubsequence(String str1, String str2) {

str1 = str1.toLowerCase();

str2 = str2.toLowerCase();

int m = str1.length();

int n = str2.length();

int[][] L = new int[m+1][n+1];

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

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

if (i == 0 || j == 0)

L[i][j] = 0;

else if (str1.charAt(i-1) == str2.charAt(j-1))

L[i][j] = L[i-1][j-1] + 1;

else

L[i][j] = Math.max(L[i-1][j], L[i][j-1]);

}

}

int index = L[m][n];

int temp = index;

char[] lcs = new char[index+1];

lcs[index] = '\t';

int i = m, j = n;

while (i > 0 && j > 0) {

if (str1.charAt(i-1) == str2.charAt(j-1)) {

lcs[index-1] = str1.charAt(i-1);

i--;

j--;

index--;

}

else if (L[i-1][j] > L[i][j-1])

i--;

else

j--;

}

System.out.print("Longest Common Subsequence of " + str1 + " and " + str2 + " is ");

for(int k=0;k<=temp;k++)

System.out.print(lcs[k]);

}

public static void main (String[] args) {

Scanner sc = new Scanner(System.in);

System.out.println("Enter the first string: ");

String str1 = sc.nextLine();

System.out.println("Enter the second string: ");

String str2 = sc.nextLine();

longestCommonSubsequence(str1, str2);

}

}

1 import java.util.Scanner; 2 3 public class Main f public static void longestCommonSubsequence (String str1, String str2) { 40 str1 str1.toLowe rCase (); str2 str2.toLowe rCase (); int m-str1. length) int n-str2. length); intD L new int[m+1] [n+1]; for (int i-0; ic«m; i++ ) { for (int j-0; jen; j+ ) { if (i -0 1 j- L[i][j] 0 else if (str1.charAt (i-1) 6 7 8 10 11 12 0) 13 str2.charAt(j-1)) 14 LLiJil Li-1][j-1] + 1; 15 else 16 Math.maxL[i-1][j], L [i][j-1]); L[i][i] 17 18 19 20 21 int index - L[m][n]; int temp index; 22 Console EProgress Debug @Javadoc Declaration Search Problems <terminated> Main (2) [Java Application] /Library/Java/JavaVirtualMachines/jd k1.8.0_144.jdk/Contents/Home/bin/java (02-No Enter the first string: saginaw Enter the second string: gain Longest Common Subsequence of saginaw and gain is gin

NOTE: Two strings can have more than one LCS, hence the output might differ from the one you provided.