Create Longest Common Subsequence.java

Longest Common Subsequence.java

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+Given two strings text1 and text2, return the length of their longest common subsequence. If there is no common subsequence, return 0.
+
+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.
+
+For example, "ace" is a subsequence of "abcde".
+A common subsequence of two strings is a subsequence that is common to both strings.
+
+
+
+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.
+
+Solution:
+
+class Solution {
+    int[][] dp;
+    public int longestCommonSubsequence(String text1, String text2) {
+        dp = new int[text1.length()][text2.length()];
+        for(int i = 0; i<dp.length; i++){
+            Arrays.fill(dp[i],-1);    
+        }
+
+        return helper(text1,text2,0,0);
+    }
+
+    public int helper(String t1, String t2, int a, int b){
+        if (a>=t1.length() || b>=t2.length()){
+            return 0;
+        }if (dp[a][b]>=0){
+            return dp[a][b];
+        }
+        if (t1.charAt(a)==t2.charAt(b)){
+            int temp = 1+helper(t1,t2,a+1,b+1);
+            dp[a][b]=temp; return temp;
+        }
+        int t = Math.max(helper(t1,t2,a,b+1),helper(t1,t2,a+1,b));
+        dp[a][b]=t; return t;
+    }
+
+}