add comments on b-tree

Author: xiaoningning

BTree/src/BTree.java

@@ -255,6 +255,7 @@ public static BTree leftMostNode(BTree node) {
         return node;
     }
 
+    // left, root, right
     public static BTree inorderSuc(BTree root, int k) {
         if (root == null)
             return null;
@@ -282,7 +283,7 @@ public static BTree inorderSuc(BTree root, int k) {
 
         }
     }
-
+    //root, left, right
     public static BTree preorderSuc(BTree node, int k) {
         if (node == null)
             return null;
@@ -322,7 +323,7 @@ else if (node.right != null)
 
 
     }
-
+    // left, right, root
     public static BTree postorderSuc(BTree root, int k) {
         if (root == null)
             return null;

PuzzleCoding/src/MergeSortedArray.java

@@ -68,6 +68,7 @@ private void shiftDown(int k) {
             while (2 * k <= heap.size() - 1) {
                 int i = 2 * k; //left
                 int j = i + 1; //right
+                //find the smallest of left and right
                 if (i < heap.size() - 1 && greater(i, j)) {
                     i++;
                 }

StringOps/src/StringOps.java

@@ -204,7 +204,7 @@ public static String rotateString(String s, int k) {
     }
 
     public static boolean isRexMatch(String s1, String s2) {
-        if (s1 == null || s1.isEmpty() || s2 == null) return false;
+        if (s1 == null || s2 == null) return false;
         if (s2.isEmpty()) return s2.isEmpty();    // "" , ""