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一、二叉树的前序遍历
1、递归实现:
public List<Integer> preorderTraversal(TreeNode root) {
// write your code here
List<Integer> list = new ArrayList<>();
preorderTraversal(root , list);
return list;
}
public void preorderTraversal(TreeNode root , List<Integer> list){
if(root == null)
return;
list.add(root.val);
preorderTraversal(root.left , list);
preorderTraversal(root.right , list);
}
2、非递归实现,利用栈
public List<Integer> preorderTraversal(TreeNode root) {
// write your code here
List<Integer> list = new ArrayList<>();
if(root == null)
return list;
Stack<TreeNode> stack = new Stack<>();
stack.push(root);
while(!stack.isEmpty()){
TreeNode node = stack.pop();
list.add(node.val);
//注意这里先压右栈,再压左栈,与前序遍历相反
if(node.right != null)
stack.push(node.right);
if(node.left != null)
stack.push(node.left);
}
return list;
}
二、二叉树的中序遍历
1、递归实现
public List<Integer> inorderTraversal(TreeNode root) {
// write your code here
List<Integer> list = new ArrayList<>();
inorderTraversal(root , list);
return list;
}
public void inorderTraversal(TreeNode root , List<Integer> list){
if(root == null)
return;
inorderTraversal(root.left , list);
list.add(root.val);
inorderTraversal(root.right , list);
}
2、非递归实现