先序、中序和后序数组两两结合重构二叉树
先序、中序和后序数组两两结合重构二叉树
java代码
package com.lizhouwei.chapter3;
import java.util.HashMap;
import java.util.Map;
/**
* @Description:先序、中序和后序数组两两结合重构二叉树
* @Author: lizhouwei
* @CreateDate: 2018/4/16 19:53
* @Modify by:
* @ModifyDate:
*/
public class Chapter3_21 {
//前序和中序数组组成二叉树
public Node preInToTree(int[] pre, int[] in) {
if (pre == null || in == null) {
return null;
}
Map<Integer, Integer> map = new HashMap<>();
for (int i = 0; i < in.length; i++) {
map.put(in[i], i);
}
return preAndIn(pre, 0, pre.length - 1, in, 0, in.length - 1, map);
}
public Node preAndIn(int[] pre, int preStart, int preEnd, int[] in, int inStart, int inEnd, Map<Integer, Integer> map) {
if (preStart > preEnd) {
return null;
}
int value = pre[preStart];
Node head = new Node(value);
int index = map.get(value);
head.left = preAndIn(pre, preStart + 1, preStart + index - inStart, in, inStart, index - 1, map);
head.right = preAndIn(pre, preStart + index - inStart + 1, preEnd, in, index + 1, inEnd, map);
return head;
}
//中序和后序数组组成二叉树
public Node inPosToTree(int[] in, int[] pos) {
if (in == null || pos == null) {
return null;
}
Map<Integer, Integer> map = new HashMap<>();
for (int i = 0; i < in.length; i++) {
map.put(in[i], i);
}
return inAndPos(in, 0, in.length - 1, pos, 0, pos.length - 1, map);
}
public Node inAndPos(int[] in, int inStart, int inEnd, int[] pos, int posStart, int posEnd, Map<Integer, Integer> map) {
if (posStart > posEnd) {
return null;
}
int value = pos[posEnd--];
Node head = new Node(value);
int index = map.get(value);
head.left = inAndPos(in, inStart, index - 1, pos, posStart, posStart + index - inStart - 1, map);
head.right = inAndPos(in, index + 1, inEnd, pos, posStart + index - inStart, posEnd, map);
return head;
}
//前序和后序数组组成二叉树
public Node prePosToTree(int[] pre, int[] pos) {
if (pre == null || pos == null) {
return null;
}
Map<Integer, Integer> map = new HashMap<>();
for (int i = 0; i < pos.length; i++) {
map.put(pos[i], i);
}
return preAndPos(pre, 0, pre.length - 1, pos, 0, pos.length - 1, map);
}
public Node preAndPos(int[] pre, int preStart, int preEnd, int[] pos, int posStart, int posEnd, Map<Integer, Integer> map) {
if (preStart > preEnd) {
return null;
}
int value = pos[posEnd--];
Node head = new Node(value);
if (preStart == preEnd) {
return head;
}
int index = map.get(pre[++preStart]);
head.left = preAndPos(pre, preStart, preStart + index - posStart, pos, posStart, index, map);
head.right = preAndPos(pre, preStart + index - posStart + 1, preEnd, pos, index + 1, posEnd, map);
return head;
}
//测试
public static void main(String[] args) {
Chapter3_21 chapter = new Chapter3_21();
int[] pre = {5, 2, 1, 3, 4, 8, 6, 7, 9, 10};
int[] in = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int[] pos = {1, 4, 3, 2, 7, 6, 10, 9, 8, 5};
Node head = chapter.preInToTree(pre, in);
System.out.println("前序数组:pre = {5, 2, 1, 3, 4, 8, 6, 7, 9, 10}");
System.out.println("中序数组:in = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}");
System.out.println("后序数组:pos = {1, 4, 3, 2, 7, 6, 10, 9, 8, 5}");
System.out.println();
System.out.println("前序数组和中序数组组成的二叉树:");
System.out.print("二叉树前序遍历:");
NodeUtil.preOrder(head);
System.out.print("二叉树中序遍历:");
NodeUtil.inOrder(head);
System.out.println();
head = chapter.inPosToTree(in, pos);
System.out.println("后序数组和中序数组组成的二叉树:");
System.out.print("二叉树后序遍历:");
NodeUtil.postOrder(head);
System.out.print("二叉树中序遍历:");
NodeUtil.inOrder(head);
System.out.println();
head = chapter.prePosToTree(pre, pos);
System.out.println("前序数组和后序数组组成的二叉树:");
System.out.print("二叉树前序遍历:");
NodeUtil.preOrder(head);
System.out.print("二叉树后序遍历:");
NodeUtil.postOrder(head);
}
}