PopulatingNextRightPointersinEachNode

Change-Id: Ifc5dbb3901954dd5d95be941737865e5a65f360c

Author: applewjg

PopulatingNextRightPointersinEachNode.java

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+/*
+ Author:     King, [email protected]
+ Date:       Oct 7, 2014
+ Problem:    Populating Next Right Pointers in Each Node
+ Difficulty: Easy
+ Source:     http://leetcode.com/onlinejudge#question_116
+ Notes:
+ Given a binary tree
+ struct TreeLinkNode {
+    TreeLinkNode *left;
+    TreeLinkNode *right;
+    TreeLinkNode *next;
+ }
+ Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.
+ Initially, all next pointers are set to NULL.
+ Note:
+ You may only use constant extra space.
+ You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).
+ For example,
+ Given the following perfect binary tree,
+      1
+    /  \
+   2    3
+  / \  / \
+ 4  5  6  7
+ After calling your function, the tree should look like:
+      1 -> NULL
+    /  \
+   2 -> 3 -> NULL
+  / \  / \
+ 4->5->6->7 -> NULL
+
+ Solution: 1. Iterative: Two 'while' loops.
+           2. Iterative: Queue. Use extra space.
+           3. Recursive: DFS. Defect: Use extra stack space for recursion.
+ */
+
+/**
+ * Definition for binary tree with next pointer.
+ * public class TreeLinkNode {
+ *     int val;
+ *     TreeLinkNode left, right, next;
+ *     TreeLinkNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public void connect(TreeLinkNode root) {
+        if (root == null) return;
+        TreeLinkNode dummy = new TreeLinkNode(-1);
+        TreeLinkNode pre = dummy;
+        TreeLinkNode cur = root;
+        while (cur != null) {
+            if (cur.left != null) {
+                pre.next = cur.left;
+                pre = pre.next;
+            }
+            if (cur.right != null) {
+                pre.next = cur.right;
+                pre = pre.next;
+            }
+            cur = cur.next;
+        }
+        connect(dummy.next);
+    }
+}

PopulatingNextRightPointersinEachNodeII.java

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+/*
+ Author:     King, [email protected]
+ Date:       Oct 7, 2014
+ Problem:    Populating Next Right Pointers in Each Node II
+ Difficulty: Easy
+ Source:     https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/
+ Notes:
+ Follow up for problem "Populating Next Right Pointers in Each Node".
+ What if the given tree could be any binary tree? Would your previous solution still work?
+ Note:
+ You may only use constant extra space.
+ For example,
+ Given the following binary tree,
+     1
+    /  \
+   2    3
+  / \    \
+ 4   5    7
+ After calling your function, the tree should look like:
+     1 -> NULL
+    /  \
+   2 -> 3 -> NULL
+  / \    \
+ 4-> 5 -> 7 -> NULL
+
+ Solution: 1. iterative way with CONSTANT extra space.
+           2. iterative way + queue. Contributed by SUN Mian(孙冕).
+           3. recursive solution.
+ */
+
+/**
+ * Definition for binary tree with next pointer.
+ * public class TreeLinkNode {
+ *     int val;
+ *     TreeLinkNode left, right, next;
+ *     TreeLinkNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public void connect(TreeLinkNode root) {
+        if (root == null) return;
+        TreeLinkNode dummy = new TreeLinkNode(-1);
+        TreeLinkNode pre = dummy;
+        TreeLinkNode cur = root;
+        while (cur != null) {
+            if (cur.left != null) {
+                pre.next = cur.left;
+                pre = pre.next;
+            }
+            if (cur.right != null) {
+                pre.next = cur.right;
+                pre = pre.next;
+            }
+            cur = cur.next;
+        }
+        connect(dummy.next);
+    }
+}