一.递归进行遍历
//前序遍历
public void preOrder(TreeNode root,List<Integer> list){
if(root==null){
return ;
}
list.add(root.val);
preOrder(root.left,list);
preOrder(root.right,list);
}
//中序遍历
public void inOrder(TreeNode root,List<Integer> list){
if(root==null){
return;
}
inOrder(root.left,list);
list.add(root.val);
inOrder(root.right,list);
}
//后序遍历
public void posOrder(TreeNode root,List<Integer> list){
if(root==null)
return;
posOrder(root.left,list);
posOrder(root.right,list);
list.add(root.val);
}
二.非递归进行遍历
//前序遍历
public void preOrder(TreeNode root,List<Integer> list){
Stack<TreeNode> stack= new Stack<>();
stack.add(root);
while(!stack.isEmpty()){
TreeNode head=stack.pop();
list.add(head.val);
if(head.right!=null){
stack.push(head.right);
}
if(head.left!=null){
stack.push(head.left);
}
}
}
//中序遍历
public void inOrder(TreeNode root,List<Integer> list){
Stack<TreeNode> stack=new Stack<>();
while(!stack.isEmpty()||root!=null){
if(root!=null){
stack.push(root);
root=root.left;
}else{
root=stack.pop();
list.add(root.val);
root=root.right;
}
}
}
//后序遍历
public void posOrder(TreeNode root,List<Integer> list){
Stack<TreeNode> s1=new Stack<>();
Stack<TreeNode> s2=new Stack<>();
s1.add(root);
while(!s1.isEmpty()){
root=s1.pop();
s2.push(root);
if(root.left!=null)
s1.push(root.left);
if(root.right!=null)
s1.push(root.right);
}
while(!s2.isEmpty()){
list.add(s2.pop().val);
}
}