一、概述
实现二叉树的前中后序遍历,达到要求:
O(1)空间复杂度,即只能使用常数空间;
二叉树的形状不能被破坏(中间过程允许改变其形状)。
二、代码详解
/**
* Morris遍历
* @author superman
*
*/
public class MorrisTraversal {
public static void process(Node head) {
if(head == null) {
return;
}
// 1
//System.out.println(head.value);
process(head.left);
// 2
//System.out.println(head.value);
process(head.right);
// 3
//System.out.println(head.value);
}
public static class Node {
public int value;
Node left;
Node right;
public Node(int data) {
this.value = data;
}
}
public static void morrisIn(Node head) {
if (head == null) {
return;
}
Node cur1 = head;
Node cur2 = null;
while (cur1 != null) {
cur2 = cur1.left;
if (cur2 != null) {
while (cur2.right != null && cur2.right != cur1) {
cur2 = cur2.right;
}
if (cur2.right == null) {
cur2.right = cur1;
cur1 = cur1.left;
continue;
} else {
cur2.right = null;
}
}
System.out.print(cur1.value + " ");
cur1 = cur1.right;
}
System.out.println();
}
public static void morrisPre(Node head) {
if (head == null) {
return;
}
Node cur1 = head;
Node cur2 = null;
while (cur1 != null) {
cur2 = cur1.left;
if (cur2 != null) {
while (cur2.right != null && cur2.right != cur1) {
cur2 = cur2.right;
}
if (cur2.right == null) {
cur2.right = cur1;
System.out.print(cur1.value + " ");
cur1 = cur1.left;
continue;
} else {
cur2.right = null;
}
} else {
System.out.print(cur1.value + " ");
}
cur1 = cur1.right;
}
System.out.println();
}
public static void morrisPos(Node head) {
if (head == null) {
return;
}
Node cur1 = head;
Node cur2 = null;
while (cur1 != null) {
cur2 = cur1.left;
if (cur2 != null) {
while (cur2.right != null && cur2.right != cur1) {
cur2 = cur2.right;
}
if (cur2.right == null) {
cur2.right = cur1;
cur1 = cur1.left;
continue;
} else {
cur2.right = null;
printEdge(cur1.left);
}
}
cur1 = cur1.right;
}
printEdge(head);
System.out.println();
}
public static void printEdge(Node head) {
Node tail = reverseEdge(head);
Node cur = tail;
while (cur != null) {
System.out.print(cur.value + " ");
cur = cur.right;
}
reverseEdge(tail);
}
public static Node reverseEdge(Node from) {
Node pre = null;
Node next = null;
while (from != null) {
next = from.right;
from.right = pre;
pre = from;
from = next;
}
return pre;
}
// for test -- print tree
public static void printTree(Node head) {
System.out.println("Binary Tree:");
printInOrder(head, 0, "H", 17);
System.out.println();
}
public static void printInOrder(Node head, int height, String to, int len) {
if (head == null) {
return;
}
printInOrder(head.right, height + 1, "v", len);
String val = to + head.value + to;
int lenM = val.length();
int lenL = (len - lenM) / 2;
int lenR = len - lenM - lenL;
val = getSpace(lenL) + val + getSpace(lenR);
System.out.println(getSpace(height * len) + val);
printInOrder(head.left, height + 1, "^", len);
}
public static String getSpace(int num) {
String space = " ";
StringBuffer buf = new StringBuffer("");
for (int i = 0; i < num; i++) {
buf.append(space);
}
return buf.toString();
}
public static void main(String[] args) {
Node head = new Node(4);
head.left = new Node(2);
head.right = new Node(6);
head.left.left = new Node(1);
head.left.right = new Node(3);
head.right.left = new Node(5);
head.right.right = new Node(7);
printTree(head);
morrisIn(head);
morrisPre(head);
morrisPos(head);
printTree(head);
}
}