LeetCode 872 Leaf-Similar Trees

栏目: 数据库 · 发布时间: 7年前

内容简介：给定两颗二叉树, 判断其叶子节点的序列是否是一致的.例:本题主要考察的是对树的遍历，遍历获取所有叶子节点，并比较是否一致即可。下面给出递归和非递归两种实现方式。

给定两颗二叉树, 判断其叶子节点的序列是否是一致的.

例:

树1:
        4
       / \
      2   7
     / \
    1   3

叶子节点序列为 [1, 3, 7]

树2:
        9
       / \
      6   7
     / \
    1   3

叶子节点序列为 [1, 3, 7]


两棵树叶子节点序列相同, 返回 true.

解法

本题主要考察的是对树的遍历，遍历获取所有叶子节点，并比较是否一致即可。下面给出递归和非递归两种实现方式。

递归写法 (DFS):

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean leafSimilar(TreeNode root1, TreeNode root2) {
        ArrayList<Integer> list1 = new ArrayList<>();
        ArrayList<Integer> list2 = new ArrayList<>();
        dfs(root1, list1);
        dfs(root2, list2);
        return list1.equals(list2);
    }

    private void dfs(TreeNode root, ArrayList<Integer> list) {
        if (root == null) {
            return;
        }

        if (root.left == null && root.right == null) {
            list.add(root.val);
        }

        dfs(root.left, list);
        dfs(root.right, list);
    }
}

Runtime: 0 ms, faster than 100.00% of Java online submissions for Leaf-Similar Trees.
Memory Usage: 37.3 MB, less than 6.16% of Java online submissions for Leaf-Similar Trees.

非递归写法:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution2 {
    public boolean leafSimilar(TreeNode root1, TreeNode root2) {
        ArrayList<Integer> list1 = new ArrayList<>();
        ArrayList<Integer> list2 = new ArrayList<>();

        pushLeafRoot(root1, list1);
        pushLeafRoot(root2, list2);
        return list1.equals(list2);
    }

    private void pushLeafRoot(TreeNode root, ArrayList<Integer> list) {
        if (root == null) {
            return;
        }

        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);

        while (!stack.isEmpty()) {
            TreeNode node = stack.pop();

            if (node.left != null) {
                stack.push(node.left);
            }
            if (node.right != null) {
                stack.push(node.right);
            }

            if (node.left == null && node.right == null) {
                list.add(node.val);
            }
        }
    }
}

Runtime: 1 ms, faster than 82.41% of Java online submissions for Leaf-Similar Trees.
Memory Usage: 36.7 MB, less than 71.02% of Java online submissions for Leaf-Similar Trees.

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