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Solution032.java
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Solution032.java
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package com.portgas;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
public class Solution032 {
public static class TreeNode {
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int val) {
this.val = val;
}
}
/**
* 从上往下打印二叉树:
* 从上往下打印出二叉树的每个节点,同层节点从左至右打印。
**/
public ArrayList<Integer> printFromTopToBottom(TreeNode root) {
if (root == null) {
return new ArrayList<>();
}
ArrayList<Integer> ret = new ArrayList<>();
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()) {
TreeNode treeNode = queue.poll();
ret.add(treeNode.val);
if (treeNode.left != null) {
queue.add(treeNode.left);
}
if (treeNode.right != null) {
queue.add(treeNode.right);
}
}
return ret;
}
/**
* 把二叉树打印成多行:
* 从上到下按层打印二叉树,同一层结点从左至右输出。每一层输出一行。
**/
ArrayList<ArrayList<Integer>> print(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
if (pRoot == null) {
return ret;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.add(pRoot);
while (!queue.isEmpty()) {
int layerSize = queue.size();
ArrayList<Integer> layer = new ArrayList<>();
while (layerSize-- > 0) {
TreeNode node = queue.poll();
layer.add(node.val);
if (node.left != null) {
queue.add(node.left);
}
if (node.right != null) {
queue.add(node.right);
}
}
ret.add(layer);
}
return ret;
}
/**
* 按之字形顺序打印二叉树:
* 请实现一个函数按照之字形打印二叉树,即第一行按照从左到右的顺序打印,
* 第二层按照从右至左的顺序打印,第三行按照从左到右的顺序打印,其他行以此类推。
**/
public ArrayList<ArrayList<Integer>> print2(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
if (pRoot == null) {
return ret;
}
Stack<TreeNode> s1 = new Stack<>(); // odd
s1.add(pRoot);
Stack<TreeNode> s2 = new Stack<>(); // even
while (!s1.isEmpty() || !s2.isEmpty()) {
if (!s1.isEmpty()) {
// odd
ArrayList<Integer> layer = new ArrayList<>();
while (!s1.isEmpty()) {
TreeNode p = s1.pop();
layer.add(p.val);
if (p.left != null) {
s2.add(p.left);
}
if (p.right != null) {
s2.add(p.right);
}
}
ret.add(layer);
} else {
// even
ArrayList<Integer> layer = new ArrayList<>();
while (!s2.isEmpty()) {
TreeNode p = s2.pop();
if (p.right != null) {
s1.add(p.right);
}
if (p.left != null) {
s1.add(p.left);
}
layer.add(p.val);
}
ret.add(layer);
}
}
return ret;
}
}