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Longest Common Subsequence

Updated: Mar 25, 2021

Given two strings text1 and text2, return the length of their longest common subsequence.

A subsequence of a string is a new string generated from the original string with some characters(can be none) deleted without changing the relative order of the remaining characters. (eg, "ace" is a subsequence of "abcde" while "aec" is not). A common subsequence of two strings is a subsequence that is common to both strings.

If there is no common subsequence, return 0.


Example 1:

Input: text1 = "abcde", text2 = "ace" 
Output: 3  
Explanation: The longest common subsequence is "ace" and its length is 3.

Example 2:

Input: text1 = "abc", text2 = "abc"
Output: 3
Explanation: The longest common subsequence is "abc" and its length is 3.

Example 3:

Input: text1 = "abc", text2 = "def"
Output: 0
Explanation: There is no such common subsequence, so the result is 0.

Constraints:

  • 1 <= text1.length <= 1000

  • 1 <= text2.length <= 1000

  • The input strings consist of lowercase English characters only.

Solution:


class Solution {
    public int longestCommonSubsequence(String text1, String text2) {
        
        int[][] result = new int[text1.length()+1][text2.length()+1];
        
       for(int i=1;i<=text1.length();i++)
       {
           for(int j=1;j<=text2.length();j++)
           {
              if(text1.charAt(i-1)==text2.charAt(j-1))
              {
                   result[i][j] = result[i-1][j-1]+1;
              }
               else
               {
                result[i][j] = Math.max(result[i-1][j],result[i][j-1]);
               }
              
           }
       }
        
        return result[text1.length()][text2.length()];
        
    }
    

}

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