二叉树的遍历
二叉树的前序，中序，后序，层序遍历
package 剑指offer;import java.util.ArrayList;import java.util.LinkedList;import java.util.Queue;/** * @author WangXiaoeZhe * @Date: Created in 2019/11/22 18:11 * @description: */public class Main17 { public class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null; public TreeNode(int val) { this.val = val; } } ArrayList<Integer> resultList = new ArrayList<>(); /** * 前序遍历:ABDEC * 1.首先遍历左子树,遍历到叶子结点为止 * @return * */ public boolean preorderTraverse(TreeNode node) { //首先从根节点开始遍历 resultList.add(node.val); if (node.left != null) { preorderTraverse(node.left); } if (node.right != null) { preorderTraverse(node.right); } return true; } /** * 中序遍历:DBEAC * @return * * */ public boolean inorderTarverse(TreeNode node) { if (node.left != null) { inorderTarverse(node.left); } resultList.add(node.val); if (node.right != null) { inorderTarverse(node.right); } return true; } /** * 后序遍历:DEBCA * @return * * */ public boolean postorderTarverse(TreeNode node) { if (node.left != null) { postorderTarverse(node.left); } if (node.right != null) { postorderTarverse(node.right); } resultList.add(node.val); return true; } /** * 层序遍历 * * @param root * @return */ public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) { if (root == null) { return resultList; } Queue<TreeNode> q = new LinkedList<>(); q.add(root); while (!q.isEmpty()) { TreeNode nowNode = q.peek(); q.poll(); resultList.add(nowNode.val); if (nowNode.left != null) { q.add(nowNode.left); } if (nowNode.right != null) { q.add(nowNode.right); } } return resultList; }}