// 前序遍历顺序:中-左-右,入栈顺序:中-右-左 class Solution { public List<Integer> preorderTraversal(TreeNode root) { List<Integer> result = new ArrayList<>(); if (root == null){ return result; } Stack<TreeNode> stack = new Stack<>(); stack.push(root); while (!stack.isEmpty()){ TreeNode node = stack.pop(); result.add(node.val); if (node.right != null){ stack.push(node.right); } if (node.left != null){ stack.push(node.left); } } return result; } } // 中序遍历顺序: 左-中-右 入栈顺序: 左-右 class Solution { public List<Integer> inorderTraversal(TreeNode root) { List<Integer> result = new ArrayList<>(); if (root == null){ return result; } Stack<TreeNode> stack = new Stack<>(); TreeNode cur = root; while (cur != null || !stack.isEmpty()){ if (cur != null){ stack.push(cur); cur = cur.left; }else{ cur = stack.pop(); result.add(cur.val); cur = cur.right; } } return result; } } // 后序遍历顺序 左-右-中 入栈顺序:中-左-右 出栈顺序:中-右-左, 最后翻转结果 class Solution { public List<Integer> postorderTraversal(TreeNode root) { List<Integer> result = new ArrayList<>(); if (root == null){ return result; } Stack<TreeNode> stack = new Stack<>(); stack.push(root); while (!stack.isEmpty()){ TreeNode node = stack.pop(); result.add(node.val); if (node.left != null){ stack.push(node.left); } if (node.right != null){ stack.push(node.right); } } Collections.reverse(result); return result; } }
标签:node,遍历,cur,迭代,result,null,root,stack,二叉树 From: https://www.cnblogs.com/fulaien/p/16906354.html