Mergesort fixes

Author: lee-naish

src/algorithms/controllers/msort_lista_td.js

@@ -837,8 +837,8 @@ cur_right, c_stk) => {
 
     // XXXXXXXXX
     Indices = ['i'];
-    Heads = ['Head(i) (data)'];
-    Tails = ['Tail(i) (next)'];
+    Heads = ['i.head (data)'];
+    Tails = ['i.tail (next)'];
     simple_stack = [];
 
     for (let i = 1; i<entire_num_array.length; i++) {

src/algorithms/pseudocode/msort_lista_td.js

@@ -38,8 +38,8 @@ Mergesort(L, len) \\B Main
 \\Code{
 split
     Mid <- mid point of L \\Ref scan
-    R <- tail(Mid)    // R starts after Mid
-    tail(Mid) <- Null // truncate L after Mid \\B tail(Mid)<-Null
+    R <- Mid.tail    // R starts after Mid
+    Mid.tail <- Null // truncate L after Mid \\B tail(Mid)<-Null
 \\Code}
 
 \\Code{
@@ -49,7 +49,7 @@ scan
     \\Expl}
     for i = 1 to len/2 - 1 // while not at middle
     \\In{
-        Mid <- tail(Mid) \\B MidNext
+        Mid <- Mid.tail \\B MidNext
         \\Expl{ Skip to next element
         \\Expl}
     \\In}
@@ -81,17 +81,33 @@ MergesortR
 Merge
     Initialise M with minimum of L and R \\Ref initM
     \\Expl{ Set M to the input list with the smallest first element and
-      skip over (delete) that element for that input list.
+      skip over (delete) that element for that input list. At this point,
+      we are only interested in the first element of M, M.head -
+      conceptually it is a single element list.  We could
+      set M.tail to be the empty list, but it will be reset to another
+      value later so this is not necessary.
     \\Expl}
     E <- M // E is the end element of M \\B E
+    \\Expl{ With the normal representation of lists, M
+      will be a pointer to a list cell and E will be a pointer to the same
+      list cell. In the while loop below, the elements of M from its
+      first element up to the element pointed to by E will be the elements
+      of L and R that have been skipped over. The remaining elements of M
+      can conceptually be ignored - we could set E.tail to be the empty
+      list. The value of E.tail is not used in the whie loop and is reset
+      after the while loop.
+    \\Expl}
+    \\Note{ Best color the elements of M up to E differently from the rest
+      (which are elements of L or R as well).
+    \\Note}
     while L != Null && R != Null  \\B whileNotNull
     \\Expl{ Scan through L and R, appending elements to M.  E is always the
-        end element of M, and L and R are the remaining inputs that have
+        (conceptual) end element of M, and L and R are the remaining inputs that have
         not yet been appended.
     \\Expl}
     \\In{
         append the smaller input element to M, advance pointers \\Ref CopySmaller
-        \\Expl{ The smaller of head(L) and head(R) is appended to M.
+        \\Expl{ The smaller of L.head and R.head is appended to M.
         \\Expl}
     \\In}
     append any remaining elements onto M \\Ref CopyRest
@@ -102,18 +118,18 @@ Merge
 
 \\Code{
 initM
-    if head(L) < head(R) \\B compareHeads
+    if L.head < R.head \\B compareHeads
     \\In{
         M <- L \\B M<-L
-        L <- tail(L) \\B L<-tail(L)
+        L <- L.tail \\B L<-tail(L)
         \\Expl{ M will contain the first element of L so we skip L to
           its next element.
         \\Expl}
     \\In}
     else
     \\In{
         M <- R \\B M<-R
-        R <- tail(R) \\B R<-tail(R)
+        R <- R.tail \\B R<-tail(R)
         \\Expl{ M will contain the first element of R so we skip R to
           its next element.
         \\Expl}
@@ -122,29 +138,29 @@ initM
 
 \\Code{
 CopySmaller
-    if head(L) <= head(R) \\B findSmaller
+    if L.head <= R.head \\B findSmaller
     \\In{
-        tail(E) <- L // append L element to M
+        E.tail <- L  // append L element to M
         E <- L       // E <- end element of M
-        L <- tail(L)     // skip element in L that has been appended \\B popL
+        L <- L.tail  // skip element in L that has been appended \\B popL
     \\In}
     else
     \\In{
-        tail(E) <- R // append R element to M
+        E.tail <- R  // append R element to M
         E <- R       // E <- end element of M
-        R <- tail(R)     // skip element in R that has been appended \\B popR
+        R <- R.tail  // skip element in R that has been appended \\B popR
     \\In}
 \\Code}
 
 \\Code{
 CopyRest
     if L == Null
     \\In{
-        tail(E) <- R // append extra R elements to M \\B appendR
+        E.tail <- R // append extra R elements to M \\B appendR
     \\In}
     else
     \\In{
-        tail(E) <- L // append extra L elements to M \\B appendL
+        E.tail <- L // append extra L elements to M \\B appendL
     \\In}
 \\Code}
 

src/components/DataStructures/Array/Array1DRenderer/Array1DRenderer.module.scss

@@ -3,8 +3,18 @@
 .array_1d {
     flex-shrink: 0;
 
+    // default caption is at top; some code may use undefined styles for
+    // captions - should fix XXX
+    .top_caption {
+        caption-side: top;
+        text-align: center;
+        margin-bottom: 5px;
+        font-size: 18px;
+        // color: var(--array-2d-row-col-value-color);
+        // font-family: Menlo, "Liberation Mono", Courier, monospace;
+    }
+
     .bottom_caption {
-        // added for msort_arr_td
         caption-side: bottom;
         text-align: center;
         margin-top: 15px;
@@ -13,10 +23,11 @@
         font-family: Menlo, "Liberation Mono", Courier, monospace;
     }
 
-    .captionmsort_arr_td {
+    // used for some merge sorts and recursive DFS
+    .simple_stack_caption {
         caption-side: bottom;
         // caption-side: top;
-        text-align: right;
+        text-align: right; // so stack grows to the left
         margin-top: 70px;
         // margin-top: 0px;
     }

src/components/DataStructures/Array/Array1DRenderer/index.js

@@ -91,6 +91,7 @@ class Array1DRenderer extends Array2DRenderer {
     // wrap output in table like 2D array so we can have a caption (for
     // msort_arr_td) XXX fix indentation
     return (
+      <div>
       <table
         className={switchmode(mode())}
         style={{
@@ -258,31 +259,28 @@ class Array1DRenderer extends Array2DRenderer {
             </div>
           </motion.div>
         </tbody>
-        { // XXX I've given up trying to avoid this warning...
-          // "Whitespace text nodes cannot appear as a child of <table>. Make
-          // sure you don't have any extra whitespace between tags on each
-          // line of your source code."  Similariy div inside tbody.
-          algo === 'msort_arr_td' && listOfNumbers && (
+        { algo === 'msort_arr_td' && listOfNumbers && (
             <caption
-              className={styles.captionmsort_arr_td}
+              className={styles.simple_stack_caption}
               kth-tag="msort_arr_td_caption"
-            > Call stack (n,p):&emsp; {listOfNumbers}&emsp;&emsp; </caption>)
+            > Call stack (left,right):&emsp; {listOfNumbers}&emsp;&emsp; </caption>)
         }
         {
           algo === 'msort_arr_bup' && listOfNumbers && (
             <caption
-              className={styles.captionmsort_arr_bup}
+              className={styles.top_caption}
               kth-tag="msort_arr_bup_caption"
             > &emsp; {listOfNumbers}&emsp;&emsp; </caption>)
         }
         {
           algo === 'msort_arr_nat' && listOfNumbers && (
             <caption
-              className={styles.captionmsort_arr_nat}
+              className={styles.top_caption}
               kth-tag="msort_arr_nat_caption"
             > &emsp; {listOfNumbers}&emsp;&emsp; </caption>)
         }
       </table>
+      </div>
     );
   }
 }

src/components/DataStructures/Array/Array2DRenderer/Array2DRenderer.module.scss

@@ -232,7 +232,8 @@
   color: var(--array-2d-row-col-value-color);
 }
 
-// redefined in 1D array
+// Following not really used - these algorithms use 1D arrays and styles are
+// defined separately
 .captionmsort_arr_td {
   caption-side: bottom;
   text-align: right;

src/components/DataStructures/Array/Array2DRenderer/index.js

@@ -441,14 +441,6 @@ class Array2DRenderer extends Renderer {
                Call stack (n,p):  {listOfNumbers}  
             </caption>
           )}
-          {algo === 'msort_arr_td' && (
-            <caption
-              className={algo === 'msort_arr_td' ? styles.captionmsort_arr_td : ''}
-              kth-tag="msort_arr_td_caption"
-            >
-               Call stack (n,p):&emsp; {listOfNumbers}&emsp;&emsp;
-            </caption>
-          )}
           {algo === 'msort_lista_td' && listOfNumbers && (
             <caption
               className={algo === 'msort_lista_td' ?  styles.captionmsort_lista_td : ''}