package DynamicProgramming;

class LongestCommonSubsequence {

public static String getLCS(String str1, String str2) {

// At least one string is null

if (str1 == null || str2 == null) return null;

// At least one string is empty

if (str1.length() == 0 || str2.length() == 0) return "";

String[] arr1 = str1.split("");

String[] arr2 = str2.split("");

// lcsMatrix[i][j] = LCS of first i elements of arr1 and first j characters of arr2

int[][] lcsMatrix = new int[arr1.length + 1][arr2.length + 1];

for (int i = 0; i < arr1.length + 1; i++) lcsMatrix[i][0] = 0;

for (int j = 1; j < arr2.length + 1; j++) lcsMatrix[0][j] = 0;

for (int i = 1; i < arr1.length + 1; i++) {

for (int j = 1; j < arr2.length + 1; j++) {

if (arr1[i - 1].equals(arr2[j - 1])) {

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

} else {

lcsMatrix[i][j] =

lcsMatrix[i - 1][j] > lcsMatrix[i][j - 1] ? lcsMatrix[i - 1][j] : lcsMatrix[i][j - 1];

}

}

}

return lcsString(str1, str2, lcsMatrix);

}

public static String lcsString(String str1, String str2, int[][] lcsMatrix) {

StringBuilder lcs = new StringBuilder();

int i = str1.length(), j = str2.length();

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

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

lcs.append(str1.charAt(i - 1));

i--;

j--;

} else if (lcsMatrix[i - 1][j] > lcsMatrix[i][j - 1]) {

i--;

} else {

j--;

}

}

return lcs.reverse().toString();

}

public static void main(String[] args) {

String str1 = "DSGSHSRGSRHTRD";

String str2 = "DATRGAGTSHS";

String lcs = getLCS(str1, str2);

// Print LCS

if (lcs != null) {

System.out.println("String 1: " + str1);

System.out.println("String 2: " + str2);

System.out.println("LCS: " + lcs);

System.out.println("LCS length: " + lcs.length());

}

}

}