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理解并背诵全文
Binary Tree Inorder Traversal
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public List<Integer> (TreeNode root) { List<Integer> ans = new ArrayList<Integer>(); if (root == null) return ans; Stack<TreeNode> stack = new Stack<TreeNode>(); while (root != null) { stack.push(root); root = root.left; } while (!stack.isEmpty()) { root = stack.pop(); ans.add(root.val); root = root.right; while (root != null) { stack.push(root); root = root.left; } } return ans; }
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Binary Tree Preorder Traversal
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public List<Integer> preorderTraversal(TreeNode root) { List<Integer> ans = new ArrayList<Integer>(); if (root == null) return ans; Stack<TreeNode> stack = new Stack<TreeNode>(); stack.push(root); while (!stack.isEmpty()) { root = stack.pop(); ans.add(root.val); if (root.right != null) { stack.push(root.right); } if (root.left != null) { stack.push(root.left); } } return ans; }
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Binary Tree Postorder Traversal
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public List<Integer> postorderTraversal(TreeNode root) { List<Integer> ans = new ArrayList<Integer>(); if (root == null) return ans; Stack<TreeNode> stack = new Stack<TreeNode>(); stack.push(root); while (!stack.isEmpty()) { root = stack.pop(); ans.add(root.val); if (root.left != null) { stack.push(root.left); } if (root.right != null) { stack.push(root.right); } } Collections.reverse(ans); return ans; }
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