add comments/fix bugs

Author: xiaoningning

IntArrayOps/src/IntArrayOps.java

@@ -323,7 +323,7 @@ public static ArrayList<Integer> LIS(int[] a) {
 
             if (a[memo.getLast()] <= a[i]) {
                 path[i] = memo.getLast(); // record the index of previous smaller element
-                memo.add(i);  // record the largest element
+                memo.add(i);  // record the index of the largest element
             } else {
                 int s, e;
                 for (s = 0, e = memo.size() - 1; s < e; ) {

PuzzleCoding/src/AddBinary.java

@@ -7,25 +7,22 @@
 */
 public class AddBinary {
     public static void main(String[] args) {
-        String s1 = "11";
+        String s1 = "10";
         String s2 = "110";
 
         int result = string2Integer(s1, 2) + string2Integer(s2, 2);
         System.out.println(toBinary(result));
         result = Integer.parseInt(s1, 2) + Integer.parseInt(s2, 2);
         System.out.println(Integer.toBinaryString(result));
 
-        System.out.print(~(0 & -1));
-
-
     }
 
     public static int string2Integer(String s, int code) {
         int len = s.length();
         int result = 0;
-        for (int i = 0; i < len; ++i) {
-            int temp = Integer.valueOf(s.substring(len - i - 1, len - i));
-            result += Math.pow(code, i) * temp;
+        for (int i = len -1 ; i >=0 ; i--) {
+            int temp = Integer.valueOf(s.charAt(i)-'0');
+            result += Math.pow(code, len-1-i) * temp;
         }
         return result;
     }

PuzzleCoding/src/AddTwoNumber.java

@@ -9,8 +9,8 @@
  */
 public class AddTwoNumber {
     public static void main(String[] args) {
-        int[] a = {2, 4, 3};
-        int[] b = {6, 4};
+        int[] a = {2, 9, 3};
+        int[] b = {9, 9};
         ArrayList<Integer> result = addTwoNumber(a, b);
         System.out.println(result);
     }
@@ -25,7 +25,7 @@ public static ArrayList<Integer> addTwoNumber(int[] n1, int[] n2) {
         while (l1 >= 0 && l2 >= 0) {
             int tmp = n1[l1--] + n2[l2--] + carry;
             result.add(0, tmp % 10);
-            if ((tmp + carry) / 10 >= 1)
+            if (tmp / 10 >= 1)
                 carry = 1;
             else
                 carry = 0;
@@ -37,7 +37,7 @@ public static ArrayList<Integer> addTwoNumber(int[] n1, int[] n2) {
         while (len >= 0) {
             int tmp = n[len--] + carry;
             result.add(0, tmp % 10);
-            if ((tmp + carry) / 10 >= 1)
+            if (tmp / 10 >= 1)
                 carry = 1;
             else
                 carry = 0;

PuzzleCoding/src/BSTtoDLL.java

@@ -23,7 +23,6 @@ public static void main(String[] args) {
         Node node12 = new Node(12);
         Node node14 = new Node(14);
 
-
         root.insert(node5);
         root.insert(node6);
         root.insert(node15);
@@ -36,7 +35,6 @@ public static void main(String[] args) {
         printDll(dll);
 
         bstToDllinPlace(root);
-
         printDll(head);
 
     }
@@ -91,10 +89,8 @@ public static ArrayList<Node> bstToDLL(Node node) {
         return dll;
     }
 
-
-    static Node prev, head;
-
     // in place approach
+    static Node prev, head;
     public static void bstToDllinPlace(Node p) {
         if (p == null)
             return;
@@ -106,9 +102,9 @@ public static void bstToDllinPlace(Node p) {
         if (prev == null) {
             head = p;
         } else {
-
             prev.right = p;
         }
+
         System.out.print("parent: " + p.value + " prev: ");
         nodeToString(prev);
         System.out.print(" head: ");
@@ -135,7 +131,6 @@ public static void bstToDllinPlace(Node p) {
     public static void nodeToString(Node n) {
         if (n == null) {
             System.out.println("null");
-
         } else {
             System.out.println(n.value);
         }

PuzzleCoding/src/BTreeIterator.java

@@ -1,28 +1,34 @@
+import java.util.LinkedList;
 import java.util.NoSuchElementException;
+import java.util.Queue;
 import java.util.Stack;
 
 public class BTreeIterator {
     private Node root;
     private Stack<Node> stack;
     private Stack<Node> preOrderStack;
-    private Stack<Node> leftVisitedStack;
+    private Queue<Node> postOrderQueue;
 
     public BTreeIterator(Node n) {
         root = n;
         stack = new Stack<Node>();
-        leftVisitedStack = new Stack<Node>();
+        pushLeft(root);
+
+        // for post-order, no need for in-order
+        postOrderQueue = new LinkedList<Node>();
+        pushPostOrder(root);
+        // for pre-order
         preOrderStack = new Stack<Node>();
         preOrderStack.push(root);
-        pushLeft(root);
     }
-
+    //in-order
     public boolean hasNext() {
         return !stack.isEmpty();
     }
 
     public void reset() {
         stack.empty();
-        leftVisitedStack.empty();
+        postOrderQueue.clear();
         pushLeft(root);
     }
 
@@ -34,7 +40,7 @@ public Node next() {
         return inOrderNext();
     }
 
-    // in-order
+    // in-order : left, root, right
     public Node inOrderNext() {
         if (hasNext()) {
             Node node = stack.pop();
@@ -52,11 +58,11 @@ private void pushLeft(Node node) {
         }
     }
 
-
     public boolean hasNextPreOrder(){
         return !preOrderStack.isEmpty();
     }
 
+    //pre-order: root, left, right
     public Node preOrderNext() {
         if (!preOrderStack.isEmpty()) {
             Node node = preOrderStack.pop();
@@ -71,21 +77,23 @@ public Node preOrderNext() {
             return null;
         }
     }
-
+    public void pushPostOrder(Node n){
+        if(n == null)
+            return;
+        if(n.left != null)
+            pushPostOrder(n.left);
+        if(n.right != null)
+            pushPostOrder(n.right);
+
+        postOrderQueue.add(n);
+    }
+    public boolean hasNextPostOrder(){
+        return !postOrderQueue.isEmpty();
+    }
+    //post-order: left, right, root
     public Node postOrderNext() {
-        if (hasNext()) {
-            if (stack.peek().right == null ||
-                    leftVisitedStack.contains(stack.peek().right)) {
-
-                Node node = stack.pop();
-                return node;
-
-            } else {
-                leftVisitedStack.push(stack.peek().right);
-                pushLeft(stack.peek().right);
-                return postOrderNext();
-            }
-
+        if (!postOrderQueue.isEmpty()) {
+            return postOrderQueue.poll();
         } else {
             throw new NoSuchElementException();
         }

PuzzleCoding/src/BuildBT.java

@@ -40,6 +40,7 @@ public static Node buildBTInorderPreorder(int[] in,
         if (in.length == 0 || pre.length != in.length)
             return null;
 
+        // get index of element of inOrder
         HashMap<Integer, Integer> index = new HashMap<Integer, Integer>();
         for (int i = 0; i < in.length; i++) {
             index.put(in[i], i);

PuzzleCoding/src/ClimbStairs.java

@@ -17,6 +17,8 @@ public static void main(String[] args) {
     public static int climbStairs(int n) {
         if (0 < n && n <= 1) return n;
         else if (n <= 0) return 1;
-        else return climbStairs(n - 1) + climbStairs(n - 2) + climbStairs(n - 3); // add the last step 1 or 2 or 3.
+        else return climbStairs(n - 1)
+                    + climbStairs(n - 2)
+                    + climbStairs(n - 3); // add the last step 1 or 2 or 3.
     }
 }

PuzzleCoding/src/CombinationPermutation.java

@@ -4,11 +4,13 @@ public class CombinationPermutation {
     public static void main(String[] args) {
 
         String s = "abcd";
-        int k = 2;
+        int k = 3;
         System.out.println("Combination");
         combinationK("", s, k);
         System.out.println("Permutation");
         permutationK(s.toCharArray(), s.length(), k);
+        System.out.println("Permutation1");
+        permutationK1("", s, k);
         System.out.println("MoveInOut");
         move(s.toCharArray(), s.length(), new ArrayList<String>(), true);
 
@@ -23,6 +25,15 @@ public static void combinationK(String prefix, String s, int K) {
             combinationK(prefix + s.charAt(i), s.substring(i + 1), K - 1);
     }
 
+    public static void permutationK1(String prefix, String s, int K) {
+        if (K == 0) {
+            System.out.println(prefix);
+            return;
+        }
+        for (int i = 0; i < s.length(); ++i)
+            permutationK1(prefix + s.charAt(i), s.substring(0,i)+s.substring(i + 1), K - 1);
+    }
+
     public static void permutationK(char[] s, int n, int K) {
         if (K == 0) {
             for (int i = n; i < s.length; ++i)

PuzzleCoding/src/CombinationSum.java

@@ -1,6 +1,5 @@
 import java.util.ArrayList;
 
-
 /*
 Given a set of candidate numbers (C) and a target number (T),
 find all unique combinations in C where the candidate numbers sums to T.
@@ -19,7 +18,7 @@ All numbers (including target) will be positive integers.
 */
 public class CombinationSum {
     public static void main(String[] args) {
-        int[] a = new int[]{2, 3, 6, 7, 10};
+        int[] a = new int[]{2, 3, 5, 6, 7, 10};
         int target = 10;
 
         ArrayList<ArrayList<Integer>> results = new ArrayList<ArrayList<Integer>>();
@@ -36,7 +35,7 @@ public static void combinationSum(int[] a,
                                       ArrayList<Integer> r,
                                       ArrayList<ArrayList<Integer>> results) {
 
-
+        // find it: target == 0
         if (target == 0) {
             results.add(new ArrayList<Integer>(r));
             return;

PuzzleCoding/src/CompareArrayBST.java

@@ -6,7 +6,7 @@
  * <p/>
  * e.g [3 2 1 0  5 4 6] & [3 5 2 6 4 1 0]
  * when the BST is formed by taking the elements from the left,
- * both BST turn out to be same.
+ * both BST turn out to be same. (in-order)
  * <p/>
  * 3
  * /  \
@@ -50,6 +50,7 @@ public static boolean identicalBST(int[] a, int[] b) {
         ArrayList<Integer> bSmaller = new ArrayList<Integer>();
         ArrayList<Integer> bLarger = new ArrayList<Integer>();
 
+        //a[0] and b[0] are the roots of trees.
         for (int i = 1; i < a.length; i++) {
             if (a[i] < a[0])
                 aSmaller.add(a[i]);

PuzzleCoding/src/DecodeNumber.java

@@ -15,10 +15,11 @@
 public class DecodeNumber {
     public static void main(String[] args) {
         String s1 = "11";
-        String s2 = "2019";
+        String s2 = "2119";
+        String s3 = "116";
         decodeNumber(s1);
         decodeNumber(s2);
-
+        decodeNumber(s3);
     }
 
     public static void decodeNumber(String s) {
@@ -41,13 +42,17 @@ public static void decodeNumber(String s) {
         for (int i = 1; i < len; i++) {
             char p = s.charAt(i - 1);
             char c = s.charAt(i);
-            if (p == '0' && c != '0' && ways[i - 1] == 0) {
-                ways[i - 1] = 1;
+            if (p !='0' && ways[i - 1] == 0)
+                ways[i] = 1;
+            if ( ways[i-1] != 0) {
+                ways[i] = ways[i-1];
             }
             if (p == '1' || (p == '2' && c <= '6')) {
-                ways[i] = ways[i - 1] * 2;
-            } else
-                ways[i] = ways[i - 1];
+                if(i>=2)
+                    ways[i] = ways[i - 2] + ways[i];
+                else
+                    ways[i] = ways[i-1] + ways[i];
+            }
         }
         System.out.println(s + ":" + ways[len - 1]);
     }

PuzzleCoding/src/FindMiddleShiftedSorted.java

@@ -4,7 +4,7 @@ public class FindMiddleShiftedSorted {
     public static void main(String[] args) {
         int[] a1 = new int[]{15, 17, 1, 3, 6, 7};
         int[] a2 = new int[]{15, 16, 17, 18, 1};
-        int[] a3 = new int[]{1, 2, 3, 4};
+        int[] a3 = new int[]{1, 2, 3, 4, 5};
         findMiddleShiftedSorted(a1);
         findMiddleShiftedSorted(a2);
         findMiddleShiftedSorted(a3);

PuzzleCoding/src/GenerateParentheses.java

@@ -13,19 +13,17 @@ public static void generateParentheses(char[] prefix, int left, int right, int l
             System.out.println(String.valueOf(prefix));
             return;
         } else {
-            if (left > 0 && right >= 0) {
+            if (left > 0 ) {
                 prefix[level] = '(';
                 generateParentheses(prefix, left - 1, right, level + 1);
             }
-            if (right > 0 && left >= 0) {
+            if (right > 0 ) {
                 prefix[level] = ')';
                 generateParentheses(prefix, left, right - 1, level + 1);
             }
         }
-
     }
 
-
     public static boolean isGoodParentheses(char[] s) {
 
         int level1 = 0;

PuzzleCoding/src/GrayCode.java

@@ -84,10 +84,12 @@ public static String[] grayCode(int n) {
     public static String toBinaryString(int integer) {
         StringBuilder builder = new StringBuilder();
         int temp;
-        while (integer >= 0) { // don't 0 case
+        while (integer >= 0) { // 0 case
             temp = integer;
             integer = (temp >> 1);
             builder.append(String.valueOf(temp % 2));
+            // if insert at 0, no need to reverse
+            // builder.insert(0, String.valueOf(temp % 2));
             if(integer ==0)
                 break;
         }

PuzzleCoding/src/HanoiTower.java

@@ -54,7 +54,7 @@ public void moveDisks(int n, HanoiTower dest, HanoiTower aux) {
     }
 
     public static void main(String[] args) {
-        int N = 4;
+        int N = 3;
         HanoiTower[] towers = new HanoiTower[N];
         for (int i = 1; i <= N; i++) {
             towers[i - 1] = new HanoiTower(i);