Leetcode144(前序遍历)
//递归public static List<Integer> inorderTraversal(TreeNode root){List<Integer> list = new ArrayList<>();inorder(root,list);return list;}public static void inorder(TreeNode root,List<Integer> list) {if(root==null) {return;}list.add(root.val);inorder(root.left,list);inorder(root.right,list);}//迭代public static List<Integer> preorderTraversal(TreeNode root){List<Integer> list = new ArrayList<Integer>();Deque<TreeNode> de = new LinkedList<>();if(root==null) {return list;}de.addFirst(root);while(!de.isEmpty()) {TreeNode temp = de.peekFirst();de.pollFirst();list.add(temp.val);if(temp.right!=null) {de.addFirst(temp.right);}if(temp.left!=null) {de.addFirst(temp.left);}}return list;}
Leetcode145（后序遍历）
//迭代法
public static List<Integer> postorderTraversal(TreeNode root){List<Integer> list = new ArrayList<>();Deque<TreeNode> de = new LinkedList<>();if(root==null) {return list;}de.addFirst(root);while(!de.isEmpty()) {TreeNode temp = de.peekFirst();de.pollFirst();list.add(temp.val);if(temp.left!=null) {de.addFirst(temp.left);}if(temp.right!=null) {de.addFirst(temp.right);}}Collections.reverse(list);return list;}//递归public static List<Integer> postorderTraversal(TreeNode root){List<Integer> list = new ArrayList<>();postorder(root,list);return list;}public static void postorder(TreeNode root,List<Integer> list) {postorder(root.left,list);postorder(root.right,list);list.add(root.val);}
Leetcode94（中序遍历）
//迭代
public static List<Integer> inorderTraversal(TreeNode root){List<Integer> list = new ArrayList<>();Deque<TreeNode> de = new LinkedList<>();if(root == null) {return list;}TreeNode cur = root;while(cur!=null||!de.isEmpty()) {if(cur!=null) {de.addFirst(cur);cur = cur.left;}else {cur = de.peekFirst();list.add(cur.val);de.pollFirst();cur = cur.right;}}return list;}//递归public static List<Integer> inorderTraveral(TreeNode root){List<Integer> list = new ArrayList<>();inorder(root,list);return list; }public static void inorder(TreeNode root,List<Integer>list) {if(root==null) {return;}inorder(root.left,list);list.add(root.val);inorder(root.right,list);}
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