开发笔记:二叉树的迭代遍历以及递归遍历

public ArrayList inOrder(TreeNode root ){
ArrayList result = new ArrayList();
if(root == null){
return result;
}
result.add(root.val);
inOrder(root.left);+
inOrder(root.right);
return result;
}

public ArrayList inOrder(TreeNode root ){
ArrayList result = new ArrayList();
if(root == null){
return result;
}
inOrder(root.left);
result.add(root.val);
inOrder(root.right);
return result;
}

public ArrayList inOrder(TreeNode root ){
ArrayList result = new ArrayList();
if(root == null){
return result;
}
inOrder(root.left);
inOrder(root.right);
result.add(root.val);
return result;
}

public ArrayList preOrder(TreeNode root){
ArrayList result= new ArrayList();
Stack stack = new Stack();
if(root == null){
return result;
}
if(root != null){
stack.push(root);
result.add(root.val);
root=root.left;
}else{
root=stack.pop();
root=root.right;
}
return result;
}

public ArrayList inOrder(TreeNode root){
ArrayList result = new ArrayList();
Stack stack = new Stack();
if(root == null){
return result;
}
while(root != null || !stack.isEmpty()){
if(root != null){
stack.push(root);
root=root.left;
}else{
root= stack.pop();
result.add(root.val);
root= root.right;
}
}
return result;
}

public ArrayList postTreeNode(TreeNode root){
Stack midstack = new Stack();
Stack resultstack= new Stack() ;
ArrayList result = new ArrayList();
while(root != null || !midstack.isEmpty()){
if(root != null){
midstack.push(root);
resultstack.push(root);
root=root.right;
}else{
root=midstack.pop();
root=root.left;
}
}
while(resultstack.size() > 0){
TreeNode temp = resultstack.pop();
result.add(temp.val);
}
return result;
}