added code for longest common subsequence

longest_common_subsequence.cpp

@@ -0,0 +1,36 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+    int longestCommonSubsequence(string text1, string text2) {
+
+        int n=text1.length()+1;
+        int m=text2.length()+1;
+        vector<vector<int>>lcs(n,vector<int>(m,0));
+        for(int i=n-2;i>=0;i--)
+        {
+            for(int j=m-2;j>=0;j--)
+            {
+                if(text1[i]==text2[j])
+                {
+                    lcs[i][j]=lcs[i+1][j+1]+1;
+                }
+                else
+                {
+                    lcs[i][j]=max(lcs[i+1][j],lcs[i][j+1]);
+                }  
+            }
+        }
+        return lcs[0][0];
+    }
+
+
+
+
+
+int main()
+{
+    string  s1,s2;
+    cin>>s1>>s2;
+    cout<<longestCommonSubsequence(s1,s2);
+    return 0;
+}