Update dynamic programming.

Author: jdchoi77

docs/schedule.md

@@ -29,7 +29,7 @@
 |11/11| [Homework 2](https://emory.zoom.us/rec/share/1FzBXB8581_8fTwXZz1lCLGPquaFgE13i9TWY-f8u2wpifBzTtq4m31qAyKwTd0m.khjxck1oQ5s4K23R) | | [hw 3](https://canvas.emory.edu/courses/76034/assignments/408681) | 
 |11/16| [Network Flow](https://emory.zoom.us/rec/share/AyviVMlLixWFDeJzUC_wb__x0AvIhJN8GFlD1u_ffst-V9fIGYvqQnZgSZlJD-jB.84wsBJ68HPBVxogb) |  | [quiz 8](https://canvas.emory.edu/courses/76034/assignments/410195) |
 |11/18| [Dynamic Programming](https://emory.zoom.us/rec/share/P1k3sxxd-2GSF26EQmPjVoCU6xZ_FOOZ-yQ92yJLZASLqKxVU_0yK8lZyqEN2oCV.tzbLlckOfJrrRAyH) | [book](https://emory.gitbook.io/dsa-java/dynamic-programming), [main](../src/main/java/edu/emory/cs/dynamic), [test](../src/test/java/edu/emory/cs/dynamic) | |
-|11/23| [Dynamic Programming]() | | [quiz 9]() |
+|11/23| [Dynamic Programming](https://emory.zoom.us/rec/share/bcmHGe3DHQA-VEAzgfmv74SZsiv-NFsPVFJgxneu8akX4dufQwVdN4JxX2PFgF_z.WEJrZfqhrE3OiiAM) | | [quiz 9]() |
 
 <!--  -->
 <!-- [Shortest Path Algorithms]() | [md](), [pdf](shortest_path_algorithms.pdf), [main](../src/main/java/edu/emory/cs/graph/path/) | [quiz 8](quiz0.md#quiz-8) | -->

src/main/java/edu/emory/cs/dynamic/lcs/LCS.java

@@ -15,14 +15,12 @@
  */
 package edu.emory.cs.dynamic.lcs;
 
-/**
- * @author Jinho D. Choi ({@code jinho.choi@emory.edu})
- */
+/** @author Jinho D. Choi */
 public abstract class LCS {
     /**
      * @param a the first string.
      * @param b the second string.
-     * @return a longest common sequence of the specific strings {@code a} and {@code b}.
+     * @return a longest common sequence of the two specific strings.
      */
     public String solve(String a, String b) {
         return solve(a.toCharArray(), b.toCharArray(), a.length() - 1, b.length() - 1);
@@ -31,10 +29,9 @@ public String solve(String a, String b) {
     /**
      * @param c the first array of characters.
      * @param d the second array of characters.
-     * @param i the index of {@code c} to be compared.
-     * @param j the index of {@code d} to be compared
-     * @return a longest common sequence of the specific strings {@code c} and {@code d}.
+     * @param i the index of the character in {@code c} to be compared.
+     * @param j the index of the character in {@code d} to be compared.
+     * @return a longest common sequence of the two specific strings.
      */
     protected abstract String solve(char[] c, char[] d, int i, int j);
 }
-

src/main/java/edu/emory/cs/dynamic/lcs/LCSDynamic.java

@@ -25,29 +25,10 @@ protected String solve(char[] c, char[] d, int i, int j) {
         return solve(c, d, i, j, createTable(c, d));
     }
 
-    private String solve(char[] c, char[] d, int i, int j, int[][] table) {
-        if (i < 0 || j < 0)
-            return "";
-
-        //Found common sequence
-        if (c[i] == d[j])
-            return solve(c, d, i - 1, j - 1, table) + c[i];
-
-        //If search on String c has exhausted
-        if (i == 0) return solve(c, d, i, j - 1, table);
-        //If search on String d has exhausted
-        if (j == 0) return solve(c, d, i - 1, j, table);
-
-        //Recursively search for the table[i][j] with the largest element
-        return (table[i - 1][j] > table[i][j - 1]) ? solve(c, d, i - 1, j, table) : solve(c, d, i, j - 1, table);
-    }
-
     /**
-     * Populating lcs dynamic table of the (sub)strings c and d
-     *
-     * @param c String 1
-     * @param d String 2
-     * @return dynamic table populated by finding the lcs of c[0~i] and d[0~j]
+     * @param c the first string.
+     * @param d the second string.
+     * @return the dynamic table populated by estimating the # of LCSs in the grid of the two specific strings.
      */
     private int[][] createTable(char[] c, char[] d) {
         final int N = c.length, M = d.length;
@@ -59,5 +40,18 @@ private int[][] createTable(char[] c, char[] d) {
 
         return table;
     }
+
+    private String solve(char[] c, char[] d, int i, int j, int[][] table) {
+        if (i < 0 || j < 0) return "";
+
+        // a common sequence is found
+        if (c[i] == d[j])  return solve(c, d, i - 1, j - 1, table) + c[i];
+        // search on the first string has been exhausted
+        if (i == 0) return solve(c, d, i, j - 1, table);
+        // search on the second string has been exhausted
+        if (j == 0) return solve(c, d, i - 1, j, table);
+
+        return (table[i - 1][j] > table[i][j - 1]) ? solve(c, d, i - 1, j, table) : solve(c, d, i, j - 1, table);
+    }
 }
 

src/main/java/edu/emory/cs/dynamic/lcs/LCSRecursive.java

@@ -15,23 +15,17 @@
  */
 package edu.emory.cs.dynamic.lcs;
 
-/**
- * @author Jinho D. Choi ({@code jinho.choi@emory.edu})
- */
+/** @author Jinho D. Choi */
 public class LCSRecursive extends LCS {
     @Override
     protected String solve(char[] c, char[] d, int i, int j) {
-        if (i < 0 || j < 0)
-            return "";
-
-        if (c[i] == d[j])
-            return solve(c, d, i - 1, j - 1) + c[i];
+        if (i < 0 || j < 0) return "";
+        if (c[i] == d[j]) return solve(c, d, i - 1, j - 1) + c[i];
 
-        //Get the lcs through searching from the right of string c
+        // get the LCS between c[:i-1] and d[:j]
         String c1 = solve(c, d, i - 1, j);
-        //Get the lcs through searching from the right of string d
+        // get the LCS between c[:i] and d[:j-1]
         String d1 = solve(c, d, i, j - 1);
-
         return (c1.length() > d1.length()) ? c1 : d1;
     }
 }