通过栈（Stack）实现对树的遍历

说到数的遍历树，长期以来的第一印象都是通过递归去实现。然而今天看了某位前辈的代码，才发现使用栈去实现遍历是那么简单。理论上通过数组也是可以实现同等功能的，毕竟Stack也是通过数据去实现的。

package com.sysway.ui.widget;import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Stack;public class Traversal {/*** 通过栈实现对根节点下所有叶节点的遍历* @param root 根节点* @return 叶节点集合*/private static List<TreeNode> traversalByStack(TreeNode root) {List<TreeNode> results = new ArrayList<TreeNode>();Stack<TreeNode> stack = new Stack<TreeNode>();stack.push(root); // 将元素推入栈中while (!stack.isEmpty()) {TreeNode node = stack.pop(); // 取出栈顶元素，并将该元素从栈中删除if (node.isLeaf()) { // 如果是叶节点results.add(node);}else {List<TreeNode> childrens = node.getChildrens(); // 取非叶节点的所有子节点stack.addAll(childrens); // 将所有子节点加入栈}}return results;}/*** 通过递归实现对根节点下所有叶节点的遍历* @param root 根节点* @return 叶节点集合*/private static List<TreeNode> traversalByRecursion(TreeNode node) {List<TreeNode> results = new ArrayList<TreeNode>();if (node.isLeaf()) {results.add(node);}else {for (TreeNode children : node.getChildrens()) {results.addAll(traversalByRecursion(children));}}return results;}public static void main(String[] args) {TreeNode node1 = new TreeNode("1");TreeNode node2 = new TreeNode("2");TreeNode node3 = new TreeNode("3");TreeNode node4 = new TreeNode("4");TreeNode node5 = new TreeNode("5");TreeNode node6 = new TreeNode("6");node1.addChildren(node2, node3);node2.addChildren(node4, node5);node5.addChildren(node6);List<TreeNode> leafs = traversalByStack(node1);System.out.println("---------Stack");for (TreeNode leaf : leafs) {System.out.println(leaf.getData());}List<TreeNode> leafs2 = traversalByRecursion(node1);System.out.println("---------Recursion");for (TreeNode leaf : leafs2) {System.out.println(leaf.getData());}}}class TreeNode {private List<TreeNode> childrens;private String data;public TreeNode(String data) {this.data = data;}public void addChildren(TreeNode... children) {if (children == null || children.length < 1) {return;}if (childrens == null) {childrens = new ArrayList<TreeNode>();}childrens.addAll(Arrays.asList(children));}public List<TreeNode> getChildrens() {return childrens;}public String getData() {return data;}public boolean isLeaf() {return childrens == null || childrens.isEmpty();}
}

树的结构如图：