/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public void preorder(TreeNode root) {
if(root != null){
System.out.println(root.val);
preorder(root.left);
preorder(root.right);
}
}
public void inorder(TreeNode root) {
if(root != null){
inorder(root.left);
System.out.println(root.val);
inorder(root.right);
}
}
public void postorder(TreeNode root) {
if(root != null){
postorder(root.left);
postorder(root.right);
System.out.println(root.val);
}
}
广度优先搜索(Breadth-First-Search)从根节点开始,一层一层的访问,比较符合直观想法。
使用队列先进先出的特性,访问某一层节点后,将此层节点出队,将其子节点依次入队。如此循环。
public void BFS(TreeNode root){
if (root == null) {
return;
}
LinkedList<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode node = queue.poll();
System.out.println(node.val);
if (node.left != null)
queue.offer(node.left);
if (node.right != null)
queue.offer(node.right);
}
}
深度优先搜索(Depth-First-Search)符合计算机的处理方式,使用栈结构。
public void BFS(TreeNode root){
if (root == null) {
return;
}
LinkedList<TreeNode> stack = new LinkedList<>();
stack.push(root);
while(!stack.isEmpty()){
TreeNode node = stack.pop();
system.out.println(node.val);
if(node.right!=null)
stack.push(node.right);
if(node.left!=null)
stack.push(node.left);
}
}
参考连接:https://leetcode.com/problems/validate-binary-search-tree/solution/