【LeetCode】226.Invert Binary Tree(Easy)解题报告

【LeetCode】226.Invert Binary Tree(Easy)解题报告

题目地址：https://leetcode.com/problems/invert-binary-tree/description/
题目描述：

Invert a binary tree.
     4
   /   \
  2     7
 / \   / \
1   3 6   9
to
     4
   /   \
  7     2
 / \   / \
9   6 3   1

Solution1:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 两种：bfs和dfs
 time : O(n)
 space : O(n)
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null) return root;
        TreeNode left = invertTree(root.left);
        TreeNode right = invertTree(root.right);
        root.left = right;
        root.right = left;
        return root;
    }
}

Solution2:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 两种：bfs和dfs
 time : O(n)
 space : O(n)
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null) return root;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            for(int i=0 ; i<size ; i++){
                TreeNode cur = queue.poll();
                TreeNode temp = cur.left;
                cur.left = cur.right;
                cur.right = temp;
                if(cur.left != null) queue.offer(cur.left);
                if(cur.right != null) queue.offer(cur.right);
            }
        }
        return root;
    }
}

Date：2018年3月17日