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());
 }
 }
}