public class BTNode {
private char key;
private BTNode left, right;
public BTNode(char key) {
this(key, null, null);
}
public BTNode(char key, BTNode left, BTNode right) {
this.key = key;
this.left = left;
this.right = right;
}
public char getKey() {
return key;
}
public void setKey(char key) {
this.key = key;
}
public BTNode getLeft() {
return left;
}
public void setLeft(BTNode left) {
this.left = left;
}
public BTNode getRight() {
return right;
}
public void setRight(BTNode right) {
this.right = right;
}
}
周遊二叉樹
public class BinTree {
protected BTNode root;
public BinTree(BTNode root) {
this.root = root;
}
public BTNode getRoot() {
return root;
}
public static BTNode init() {
BTNode a = new BTNode('A');
BTNode b = new BTNode('B', null, a);
BTNode c = new BTNode('C');
BTNode d = new BTNode('D', b, c);
BTNode e = new BTNode('E');
BTNode f = new BTNode('F', e, null);
BTNode g = new BTNode('G', null, f);
BTNode h = new BTNode('H', d, g);
return h;// root
}
public static void visit(BTNode p) {
System.out.print(p.getKey() + " ");
}
protected static void preorder(BTNode p) {
if (p != null) {
visit(p);
preorder(p.getLeft());
preorder(p.getRight());
}
}
protected static void inorder(BTNode p) {
if (p != null) {
inorder(p.getLeft());
visit(p);
inorder(p.getRight());
}
}
protected static void postorder(BTNode p) {
if (p != null) {
postorder(p.getLeft());
postorder(p.getRight());
visit(p);
}
}
protected static void iterativePreorder(BTNode p) {
Stack<BTNode> stack = new Stack<BTNode>();
if (p != null) {
stack.push(p);
while (!stack.empty()) {
p = stack.pop();
visit(p);
if (p.getRight() != null)
stack.push(p.getRight());
if (p.getLeft() != null)
stack.push(p.getLeft());
}
}
}
protected static void iterativePostorder(BTNode p) {
BTNode q = p;
Stack<BTNode> stack = new Stack<BTNode>();
while (p != null) {
// 左子樹入棧
for (; p.getLeft() != null; p = p.getLeft())
stack.push(p);
// 目前節點無右子或右子已經輸出
while (p != null && (p.getRight() == null || p.getRight() == q)) {
visit(p);
q = p;// 記錄上一個已輸出節點
if (stack.empty())
return;
p = stack.pop();
}
// 處理右子
stack.push(p);
p = p.getRight();
}
}
protected static void iterativeInorder(BTNode p) {
Stack<BTNode> stack = new Stack<BTNode>();
while (p != null) {
while (p != null) {
if (p.getRight() != null)
stack.push(p.getRight());// 目前節點右子入棧
stack.push(p);// 目前節點入棧
p = p.getLeft();
}
p = stack.pop();
while (!stack.empty() && p.getRight() == null) {
visit(p);
p = stack.pop();
}
visit(p);
if (!stack.empty())
p = stack.pop();
else
p = null;
}
}
public static void main(String[] args) {
BinTree tree = new BinTree(init());
System.out.print(" Pre-Order:");
preorder(tree.getRoot());
System.out.println();
System.out.print(" In-Order:");
inorder(tree.getRoot());
System.out.println();
System.out.print("Post-Order:");
postorder(tree.getRoot());
System.out.println();
System.out.print(" Pre-Order:");
iterativePreorder(tree.getRoot());
System.out.println();
System.out.print(" In-Order:");
iterativeInorder(tree.getRoot());
System.out.println();
System.out.print("Post-Order:");
iterativePostorder(tree.getRoot());
System.out.println();
}
}
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