diff --git a/src/leo/class19/LongestCommonSubsequence.java b/src/leo/class19/LongestCommonSubsequence.java
index 51fb49f..350e4d7 100644
--- a/src/leo/class19/LongestCommonSubsequence.java
+++ b/src/leo/class19/LongestCommonSubsequence.java
@@ -66,6 +66,41 @@ public class LongestCommonSubsequence {
         }
     }
 
+    static class Recursion1 {
+        public static int longestCommonSubsequence(String s1, String s2) {
+            if (s1 == null || s2 == null || s1.length() == 0 || s2.length() == 0) {
+                return 0;
+            }
+            char[] c1 = s1.toCharArray();
+            char[] c2 = s2.toCharArray();
+            return process(c1, c2, c1.length - 1, c2.length - 1);
+        }
+
+        private static int process(char[] c1, char[] c2, int i, int j) {
+            if (i == 0 && j == 0) {
+                return c1[i] == c2[j] ? 1: 0;
+            } else if (i == 0) {
+                if (c1[i] == c2[j]) {
+                    return 1;
+                } else {
+                    return process(c1, c2, i, j - 1);
+                }
+            } else if (j == 0) {
+                if (c1[i] == c2[j]) {
+                    return 1;
+                }else {
+                    return process(c1, c2, i - 1, j);
+                }
+            }else {
+                int p1 = process(c1, c2, i - 1, j);
+                int p2 = process(c1, c2, i, j - 1);
+                int p3 = c1[i] == c2[j] ? 1 + process(c1, c2, i - 1, j - 1) : 0;
+                return Math.max(p1, Math.max(p2, p3));
+            }
+
+        }
+    }
+
     static class Dp {
         public static int longestCommonSubsequence(String s1, String s2) {
             if (s1 == null || s2 == null || s1.length() == 0 || s2.length() == 0) {
@@ -95,4 +130,34 @@ public class LongestCommonSubsequence {
         }
     }
 
+    static class Dp1 {
+        public static int longestCommonSubsequence(String s1, String s2) {
+            if (s1 == null || s2 == null || s1.length() == 0 || s2.length() == 0) {
+                return 0;
+            }
+            int n = s1.length();
+            int m = s2.length();
+            char[] c1 = s1.toCharArray();
+            char[] c2 = s2.toCharArray();
+            int[][] dp = new int[n][m];
+            dp[0][0] = c1[0] == c2[0] ? 1 : 0;
+            for (int j = 1; j < m; j++) {
+                dp[0][j] = c1[0] == c2[j] ? 1 : dp[0][j - 1];
+            }
+            for (int i = 1; i < n; i++) {
+                dp[i][0] = c1[i] == c2[0] ? 1 : dp[i - 1][0];
+            }
+            for (int i = 1; i < n; i++) {
+                for (int j = 1; j < m; j++) {
+                    int p1 = dp[i - 1][j];
+                    int p2 = dp[i][j - 1];
+                    int p3 = c1[i] == c2[j] ? 1 + dp[i - 1][j - 1] : 0;
+                    dp[i][j] = Math.max(p1, Math.max(p2, p3));
+                }
+            }
+            return dp[n - 1][m - 1];
+
+        }
+    }
+
 }