个人技术分享

题目链接

在做二叉树题目时，应该首先确定使用前序遍历 / 中序遍历 / 后序遍历 / 层序遍历

前序遍历 + 栈

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        Stack<TreeNode> stack = new Stack<TreeNode>() ;
        if(root != null){
            stack.push(root);
        }
        while(!stack.isEmpty()){
        	// 中
            TreeNode node = stack.pop();
            // 交换左右节点
            TreeNode temp = node.left;
            node.left = node.right;
            node.right = temp;
            // 右
            if(node.right != null){
                stack.push(node.right);
            }
            // 左
            if(node.left != null){
                stack.push(node.left);
            }
        }
        return root;
    }
}

层序遍历 + 栈

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        Stack<TreeNode> stack = new Stack<TreeNode>() ;
        if(root != null){
            stack.push(root);
        }
        while(!stack.isEmpty()){
            int size = stack.size();
            for(int i = 0; i < size; i++){
            	// 中
                TreeNode node = stack.pop();
                // 交换左右节点
                TreeNode temp = node.left;
                node.left = node.right;
                node.right = temp;
                // 右
                if(node.right != null){
                    stack.push(node.right);
                }
                // 左
                if(node.left != null){
                    stack.push(node.left);
                }
            }
        }
        return root;
    }
}